Wiring Aftermarket Equipment and Upgrade Components

Now the fun begins! This is the time where we get to add things to the vehicle that improve it, add functionality, or customize it to our liking. This chapter puts to work all the new skills you’ve learned to this point.

 


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When it comes to adding aftermarket electronics, there are really only two objectives:

  • Add functionality—such as adding a tach to a vehicle that does not have one already.
  • Duplicate the OEM controls—such as adding a keyless entry system to a vehicle that already has power door locks. Doing this simply adds functionality to an already existing circuit by allowing the user to control that circuit with a remote control.

Adding either of the above components can mean adding a new circuit, especially the first. In this chapter explains how to do it like the pros do every day.

 

Safety First

It should go without saying that when you’re working on a vehicle, it’s best to do so on a flat, level surface. If you need to raise the front or the rear of the vehicle in the course of the installation, then you should always support it with jack stands. In addition, you need to appropriately chock the wheels on the ground to prevent the vehicle from rolling off of the jack stands. In addition, set the emergency brake. Finally, make sure the vehicle is in park if it is an automatic and neutral if it is a stick shift.

You’ve already been educated on when and how to disconnect the vehicle’s battery should the need arise. If you need to, refer to Chapter 1 for a refresher.

 

Passing Through a Metal Barrier

Invariably, the installation of aftermarket electronics requires passing wiring through metal barriers—like the firewall. In addition, these electronics need to be securely mounted in place. Either way, this can mean that drilling or screwing through something in the process.

CAUTION: Don’t blindly drill holes or run screws through the firewall, floorboard, or even a center console without being sure that you know what’s on the other side! To do so, you risk piercing or drilling through any number of things, such as brake lines, fuel lines, and the vehicle’s wiring. Piercing a brake or fuel line creates a serious safety issue! Damage to the vehicle’s wiring harness can run into the thousands to repair!

Tools Required

In addition to the tools I out-lined extensively in Chapters 2 and 3, the following makes your job that much easier:

  • Grommet Tool
  • Drill
  • Step Drill
  • Hole Saw Kit

 

 I bought this Thexton grommet tool from the Matco guy back in the day. Notice that the shaft is hollow—push it through a grommet, push your wire through the tool, remove the tool.

I bought this Thexton grommet tool from the Matco guy back in the day. Notice that the shaft is hollow—push it through a grommet, push your wire through the tool, remove the tool.

 

Unibit makes the step drills pictured here. The small one goes from 1/8 to 1/2 inch in 1/32-inch steps, and the big one goes from 1/2 to 1 inch in 1/16-inch steps.

Unibit makes the step drills pictured here. The small one goes from 1/8 to 1/2 inch in 1/32-inch steps, and the big one goes from 1/2 to 1 inch in 1/16-inch steps.

 

This is a Magna hole saw kit. A 2-5/8-inch hole saw is also available for installing gauges of the same size.

This is a Magna hole saw kit. A 2-5/8-inch hole saw is also available for installing gauges of the same size.

 

Grommet Tool: Another one of my favorite tools is the grommet tool. This tool has a hollow shaft that is quite pointy. It has been designed to pierce through a grommet and allow you to easily run wiring through it by pushing the wiring down through the shaft of the tool.

This is one of the coolest tools I own and eliminates the “straightened out” coat hanger or the car antenna that I use to use for this arduous job years ago. Plus, you no longer need to tape your wiring to the thing you stuck through the grommet, hoping it stayed while you pulled it through from the other side.

Drill: I’m not going to spend a lot of time on this because anyone reading this book likely has four or five of them lying about. For automotive use, I prefer the cordless or air powered variety. Pick your poison, just make sure it has a 1/2-inch chuck so that you can chuck up the big stuff.

Step Drill: The number one advantage a step drill offers over a standard drill bit I the ability to drill a hole in a metal barrier without the bit racing through said hole after the bit passes through the metal. This can be a life saver. Properly used, you will never run the risk of damaging something on the other side with a step drill. Note that the step drill also provides a nice center starting point for the drill bit in a hole saw arbor. Buy one!

Hole Saw Kit: Many times, you need to drill a hole through the firewall that allows the passage of a large-gauge wire, a large wiring harness, or even a drain tube like that of an aftermarket AC system. A hole saw kit with two arbors and numerous saws like the one pictured, which makes this job so much easier. The right size hole saw also makes the installation of aftermarket gauges a snap in a dashboard.

 

Installing a Tachometer

OK, now that the basics have been covered, it’s time to get your hands dirty with one of the most common installations I can think of. Recall in Chapter 1, I discussed verifying wiring before simply connecting to it. The example I gave was that of installing a tach. This is an excellent example of how to use everything you’ve learned thus far to install a tach like a pro. In this case, we add functionality to the vehicle.

Pre-Installation

Before starting this job, let’s give the following consideration:

  • Turn the ignition switch to the off position. This is a good rule of thumb for a starting point of installing pretty much anything in your vehicle.
  • Pay special attention to the routing of your wiring. It’s always easier to follow the factory wiring harnesses when adding wiring, and this ensures that you keep it out of harm’s way. Avoid moving objects, such as the pedals and steering column, at all costs and keep your wiring away from sharp edges to avoid damaging its insulation.
  • Use an insulator to run wiring through the firewall. This protects the wiring and prevents chafing. A factory installed rubber grommet is ideal, but sometimes it is necessary for you to drill a hole and install one.
  • Properly secure or anchor all wiring that you add to a vehicle.

 

Installation

Now, let’s get down to it. In this example, we install a tachometer in a 1970 Ford Torino using a DMM to verify all of the wiring. In addition, we are using a combination of soldering and crimping for our connections to ensure many years of trouble free operation of our tach.

Let’s separate the installation into six different phases:

  • Mounting the tach.
  • Connecting to the tach signal lead under the hood at the coil.
  • Connecting to the ignition lead at the ignition switch.
  • Connecting to the dimmer lead at the parking light switch.
  • Testing the tach for correct operation.
  • Buttoning up the installation.

Mounting the Tach: (Note that it may be easier to install the tach by having access to the lower dash area.

 

This Auto Meter Sport Comp tachometer is representative of what’s on the shelf at your local speed shop. Exactly what you need to install the tach, including brackets, mounting screws, a grommet, etc., comes with the tachometer. Incidentally, the length of wire Auto Meter included proved to be right on the money because I didn’t have to extend a single wire.

This Auto Meter Sport Comp tachometer is representative of what’s on the shelf at your local speed shop. Exactly what you need to install the tach, including brackets, mounting screws, a grommet, etc., comes with the tachometer. Incidentally, the length of wire Auto Meter included proved to be right on the money because I didn’t have to extend a single wire.

 

This may require removing one or several panels to gain access. Do this prior to the start of the installation.)

Step 1:

5Mount the tach.

 
 
 
 
 
 
 

Step 2:

6Run the wiring from the tach under the vehicle’s dash.

 
 
 
 
 
 
 
 

Connecting to the tach lead under the hood at the coil: I always like to do the most difficult part of any wiring job first. Without fail, passing through the firewall can be the most challenging part of a job. Let’s get it done first.

Step 1:

7Locate a rubber grommet in the firewall that is suitable to pass the tach signal wire through.

 
 
 
 

Step 2:

Route the signal lead from the tach through this rubber grommet in the firewall to the coil and connect it to the negative side of the coil.

Step 3:

Now how do we determine which side of the coil is negative? No problem…get your DMM ready.

Step 4:

8Disconnect one of the coil wires (or the plug to the coil) and turn the ignition switch forward to the run position.

 
 
 
 
 
 

 

 I routed the wiring along the factory wiring harness whenever possible. This gives the finished product a nice, clean look.

I routed the wiring along the factory wiring harness whenever possible. This gives the finished product a nice, clean look.

Step 5:

Use your DMM to determine which of the two wires reads + 12 VDC—this means the other wire is the coil (-).

Step 6:

10Turn the Ignition switch OFF, make your connection to the coil wire, and reconnect the wiring to the coil.

 
 
 
 
 

Connecting to the Ignition Lead at the Ignition Switch:Many vehicles used to come from the factory with at least one spot in the fuse box that was intended to power a low- to medium-current accessory. GM used to provide connection points on the right side of the fuse box for a connection to constant power, labeled BAT, switched power, labeled IGN, and the dash lamps, labeled LPS. If your vehicle is so equipped, refer to the owner’s manual to verify whether these outputs are fused or not and their current capability.

In addition, as mentioned in the last chapter, some later model vehicles do not use a traditional ignition switch. Some British vehicles have low-current negative outputs for all switch positions. There are also some 2008 model vehicles with two-wire ignition switches—an input and an output that varies in voltage or ground potential based on the key’s position. As you’ll not likely be adding a 5-inch tach to your 2008 BMW 7 series, the steps I outline cover 99 percent of the vehicles you’re likely to own.

CAUTION: This step involves bumping the starter slightly, which could cause some vehicles to start. Be sure that the vehicle is not in gear, and the underhood area is clear of tools, wiring, or bystanders!

Step 1:

11Bring your DMM inside the vehicle, and place it on the floor where you can easily read its display.

 
 
 
 
 
 
 

Step 2:

12Locate the harness that comes from the ignition switch, and remove any tape or covering from it so that you can easily access the wiring to it.

 
 
 
 
 

 
 

Step 3:

Use the DMM to determine which of the BIG wires has +12 Volts on it is in the IGN/RUN position.

Step 4:

13Verify that this wire also has + 12 Volts on it when in the START position. A quick turn to START is all that is required to verify that voltage remains during this step. This is the correct wire. (In the case of this Torino, I noticed a three position female bullet-style pigtail just above the ignition switch harness with the identical color wire and electrical properties as the ignition switch itself. It would appear that Ford included this to make adding an IGN powered accessory easier.)

 

Step 5:

Turn the ignition switch to the OFF position, and solder the in-line ATC fuse holder to the wire you determined in the last step. (In this case, I crimped a male bullet to the end of the fuse holder to allow it to be plugged directly into this IGN pigtail Ford provided.)

Step 6:

14Crimp the Ignition (+) lead from the tach to the other end of the fuse holder. The fuse holder protects the wiring you’ve tied into in the event that the wiring to the tach gets pinched or damaged in some way.

 
 
 
 
 

Connecting to the Dimmer Lead at the Parking Light Switch: Access the wiring harness from your parking light switch (or dedicated dimmer switch if your vehicle has one).

 

MuscleCarB

 

Step 1:

With your DMM set up the same way as in the preceding step, use the red probe to determine which of the wires on the parking light switch has variable voltage on it with the parking lights turned on. That is, the correct wire should have voltage present on it, and it should vary from 0 to 12 VDC as you rotate the dimmer switch.

Step 2:

15Turn off the parking light switch and solder a second in-line ATC fuse holder to this wire.

 
 
 
 

Step 3:

16Route the illumination (+) lead from the tach and connect it to the other end of the fuse holder. (Note: on some vehicles, you can find a fused connection to this circuit in the fuse panel—although it may not be labeled. GM typically used LPS to denote this circuit.)

 

Step 4:

17Connect ground (-) lead from the tach to chassis ground.

 
 
 
 
 
 
 
 

Step 5:

Per the tach manufacturer’s installation instructions, install an ATC fuse in each of the fuse holders, and the tach is now ready for testing.

Testing the Tach for Correct Operation: Turn the dash lamps on. Rotate the dimmer to MAX and to MIN to verify the correct operation of the illumination of the tach. The light in the tach should follow the cue of the dash lights.

Start the vehicle and verify that the tach works correctly, and it certainly should!

Turn the ignition switch back to the OFF position and the tach should be off.

In the case of this Torino, the tach worked like a champ on the first go. In addition, the owner was pleasantly surprised to learn that the tach’s back lighting would vary with the dash lights via the dimmer—just the way it should be!

Buttoning Up the Installation: Now that you’ve gotten everything working properly, it’s time to button up the install:

Step 1:

18Using cable ties, secure your wiring to the factory wiring in such a way that it is clear of moving parts and sharp edges.

 
 
 
 

Step 2:

Re-assemble any interior pieces you removed earlier.

You just used the skills you learned in the first four chapters to successfully and safely install a tach, just like the pros would! And you did it without having a mess of spaghetti under the dash that got tangled up in the steering column and a bunch of sub-par un-fused connections.

Adding a Remote Trunk Pop Circuit

Let’s say that we had a vehicle that came equipped with an electronic trunk release button like my Mustang. Pressing this button opens the trunk of the vehicle electronically. The button is conveniently located in the glove compartment, so it is out of the way and it can be locked to prevent a would be thief from quickly accessing it.

The objective here is to interface with this circuit so that we could control it from the remote control of a generic auto security system. This is a great example of duplication the OEM controls to achieve the desired result. Here are our considerations:

  • Output of auto security system provided for such.
  • Said output is negative (-) on trigger and has 200 mA of output capability as specified by the manufacturer.
  • Trunk release circuit powers a pull type solenoid that requires far more than 200 mA to operate it.

Here’s what we need: a single Bosch relay, a few .250-inch female push-on terminals, some 18- and 16-gauge wire, and one quenching diode. Figure 6-1 is a diagram of the circuit interface to be made.

 

Figure 6-1

Figure 6-1

 

In this case, to access the wiring to the switch, it is necessary to remove the glove compartment to do so. Here’s how to make the interface:

Step 1:

Use your DMM to determine which of the two wires on the rear of the trunk release button is the trigger wire to the solenoid (only has +12 VDC when the switch is depressed). The other wire is the power wire to the switch. (In some cars, this is only live with the gear selector in park.)

Step 2:

19Determine a suitable mounting location for the relay nearby—in this example, that’s about 12 inches from the switch. Clamp the relay top down in a bench vise to pre-wire it.

 
 

Step 3:

Connect a short piece of 18-gauge red wire to the cathode of a diode and crimp a female push-on terminal to them both.

Step 4:

21Connect this to terminal 86. Connect the other end of the 18-gauge red wire to a 12-inch-long piece of red 16-gauge wire and crimp a female push-on terminal to them both.

 
 

Step 5:

22Connect this to terminal 87.

 
 
 
 
 

Step 6:

C23rimp another female push-on terminal to a 12-inch length of green 16-gauge wiring and connect this to terminal 30.

 
 
 

Step 7:

24Connect both the output from the security system and the anode of the diode to terminal 85 of the relay.

 
 
 
 
 

Step 8 :

25Tape around the body of the relay and the terminals to insulate the electrical connections from contacting any nearby metal surfaces via a push-on terminal crimped to both.

 
 
 
 

Step 9:

26Mount the relay in the vehicle with its terminals pointing down—at an angle is OK.

 
 
 
 
 
 

Step 10:

Solder the red 16 AWG wire from Terminal 87 of the relay to the power wire of the switch (no fusing necessary as this is already done in the fuse panel) and insulate this connection with Super 33+ tape.

Step 11:

27Solder the green 16 AWG wire from Terminal 30 of the relay to the solenoid wire (again, no fusing necessary) and insulate this connection with Super 33+ tape.

 
 
 

28

 
 
 
 
 

Step 12:

Test the circuit by depressing the trunk release button on the key fob—the trunk should pop.

Step 13:

29Tie your wiring up and out of harm’s way.

 
 
 
 
 
 
 
 
 

Now that you’ve verified the circuit works properly, you can reinstall the glove compartment. Congratulations—in this installation, you learned how to duplicate the OEM controls and installed a quenching diode. And all this time, you thought relays were a mystery. Well, mystery solved.

At this point, you really know how to install every piece of after-market electronics on the market. Remember, you’re either adding functionality as we did by installing a tach or you’re duplicating the OEM controls as we did by adding a remote trunk pop circuit. The logic is the same regardless of the complexity or scale of the project.

Adding A High-Current Accessory

Now let’s say that you wanted to add a high powered audio amplifier, such as the 400 Watt RMS (the only number that means anything; pay no attention to PEAK or MAX numbers because they’re meaningless) unit in my wife’s Nissan Frontier. Most manufacturers specify the cur-rent requirements of their products. If not, you can look at the fusing or recommend fusing of the amplifier(s) to make this determination.

This amplifier calls for a 60-amp fuse on its main power lead. One of the main differences between audio systems and other high-current accessories is that the same powered audio system would draw roughly half as much current on average to play music at full volume, as music typically has a 50 percent duty cycle. This is because music is dynamic in nature—it has peaks and dips in the overall volume level so the amplifier does not draw current continuously like a headlight. Rather, it consumes it as it is required. Assume the amplifier requires 50 percent of the fuse value to play music at full volume and 100 percent of the fuse value to reproduce test tones.

The manufacturer of this amplifier recommends 4 AWG wiring for the power and ground connections, which corresponds to the math you learned in Chapter 1. Let’s double check by doing a quick calculation for voltage drop over this length of wire, assuming you had to use 17 foot of power wire and 3 foot of ground wire:

E = I x R

E = 60 Amps x (20 x .000253 Ω)

E = 60 Amps x .00506 Ω

E = .304 Volts

This is more than acceptable. Keep in mind that you have to factor the maximum current draw from the amplifier to make this determination. Now, suppose that you wanted to know how long you could play music with this amplifier at full volume with the key off with a typical 45 AH battery—in this case, you want to consider what the amplifier consumes on average when playing music. Simple, one and a half hours:

45 AH / 30 amps = 1.5 hours. If your objective was to be able to do this for 3 hours, for instance at the picnic in the park on Memorial Day weekend, you would need a second identical battery in parallel: 90 AH / 30 amps = 3 hours. (Obviously, you’d need to play the system at a little less than full volume for this period of time if you desired to start the vehicle and drive it away versus getting a jump.) Chapter 7 explains how to do this correctly (and safely).

It is possible that the addition of this amplifier could very well exceed the current capability of your stock alternator. To determine this, increase volume to loudest point you’re likely to play it. Keep the vehicle running and measure voltage at the battery via the steps outlined in the “Upgrading the Alternator” section.

Sourcing Power for your High-Current Accessory

When you add a high current accessory, the best place to connect it is the positive post of the battery itself. I do this with any accessory that requires in excess of 15 amps of current. When connecting to the battery, observe all of the same safety considerations outlined in Chapter When speaking of automotive batteries, there are two main types—top post and side post.

Connecting to a Top-Post Battery: The correct way is to make the connection to the battery clamp as I did in Chapter 1 with the ground wire to the security system in my wife’s truck. For larger cables, you need the correct size ring terminal. In the case of the 4-gauge wire that supplies power to the amplifier in her truck, note that it connects to the positive battery terminal via way of the top bolt on the battery clamp. This provides an excellent connection.

 

This 4 AWG wiring terminated with a ring terminal connects to the stock top post connector on the Nissan Frontier. This provides a low-resistance connection that does not restrict current flow. To allow the plastic cover to fold back down over the terminal, I notched the side of it to allow the cable to exit neatly.

This 4 AWG wiring terminated with a ring terminal connects to the stock top post connector on the Nissan Frontier. This provides a low-resistance connection that does not restrict current flow. To allow the plastic cover to fold back down over the terminal, I notched the side of it to allow the cable to exit neatly.

 

Connecting an accessory power cable to a side-post battery has never been easier. The adapter on the bottom is a standard GM side post battery adapter. On the top left is a long version of the same adapter—handy for GM trucks with diesel engines and dual batteries. On the right is an adapter designed to screw into the side post of the battery directly and allow one to use a standard top-mount battery clamp. These are available in both (+) and (-) versions as the post diameters are different.

Connecting an accessory power cable to a side-post battery has never been easier. The adapter on the bottom is a standard GM side post battery adapter. On the top left is a long version of the same adapter—handy for GM trucks with diesel engines and dual batteries. On the right is an adapter designed to screw into the side post of the battery directly and allow one to use a standard top-mount battery clamp. These are available in both (+) and (-) versions as the post diameters are different.

 

Aftermarket battery clamps, such as the Lightning Audio clamps I use on the Mustang, allow you to easily connect multiple large cables to the battery. Although not visible, the set screws for each of the cables is on the bottom of the clamps. Not pictured are the plastic covers that these clamps come with.

Aftermarket battery clamps, such as the Lightning Audio clamps I use on the Mustang, allow you to easily connect multiple large cables to the battery. Although not visible, the set screws for each of the cables is on the bottom of the clamps. Not pictured are the plastic covers that these clamps come with.

 

Connecting to a Side-Post Battery: Side-post batteries have been used in GM vehicles since the early 1990s. These are equally as simple to connect to, but the connection requires a GM side post battery adapter. These are available in short and long versions (for dual battery systems in diesel trucks) and readily available at your local auto parts store. One simply removes the 8 mm battery bolt from the cable entirely and replaces it with the adapter. The adapter has a bolt on its end that allows easy connection to an accessory power wire via way of a ring terminal.

Aftermarket Battery Clamps: After-market battery clamps were designed to make adding high-current accessories, as well as upgrading the wiring in your charging system, a snap. These are typically available only for top post batteries, although there have been a handful of side post battery clamp offerings over the years as well. Sometimes, as was the case in my Mustang, the stock battery clamps have to be cut off the cables themselves to allow installation of aftermarket battery clamps. This is not a big deal, so don’t worry!

 

The Charging System—Revisited

What if you wanted to add a high-current accessory that required more amperage than the stock charging sys-tem could support right out of the gate? Simple, you upgrade it! First, you need to determine what to upgrade. Remember, the charging system consists of three simple components:

  • The Battery
  • The Alternator
  • The Return Path
  • Let’s take them in reverse order.

Upgrading the Return Path

If I’m going to add any accessories to a vehicle, I make the assumption that the factory return path is not suitable for the additional load. At minimum, add a second lead of the same size for the additional current demands of the accessories being added.

If you’re adding a high-current accessory, such as a power inverter or an audio amplifier (or a stack of’em), look at the current requirements of these devices and the size of the cables that the manufacturer either includes with them or recommends. In addition, have the same-size cable between the battery (-) and the chassis as between the battery (+) and the unit.

Let’s say that I was installing the 400 Watt RMS audio amplifier from the example above. Since I used 4 AWG wiring for the positive, this means, that I also need a return path between the amplifier (-) and the battery (-) with a minimum of 4 AWG equivalency. At the bare minimum, I would have to:

  • Connect the amplifier (-) to the chassis with 4 AWG wire.
  • Connect the battery (-) to the chassis with 4 AWG wire.

As pictured, the truck has a 4 AWG between the battery (-) and the chassis already, so this did not need to be upgraded. If I upgraded the system further down the road, it would need to be.

In some cases, you can’t reliably pass the high current required by such accessories through the chassis of the vehicle. For trucks and older cars, there is a simple solution—use the frame as the return path. This is what I chose to do with my wife’s truck, even though it really wasn’t necessary.

Even 1/0 AWG wire has far greater resistance per foot than the frame of a vehicle. For any vehicle that sits on a frame, I always use the frame for the return path when adding high-current accessories. This is easy.

My Mustang has an audio system with 3,000 Watts RMS of power, so 4-gauge or even 2-gauge won’t cut it.

This is job for 1/0 AWG!

 

It is always a good idea to upgrade the stock accessory return path. As shown, I connected a piece of 8 AWG from each of the 8 AWG outputs of the Lightning Audio battery clamps to each of the green 8-mm bolts.

It is always a good idea to upgrade the stock accessory return path. As shown, I connected a piece of 8 AWG from each of the 8 AWG outputs of the Lightning Audio battery clamps to each of the green 8-mm bolts.

 

If I’m installing a high-current accessory in any vehicle with a frame under it, I always use the frame for the return path for said accessory. As shown, white lithium grease can help to prevent such connections from corroding and/or rusting over time.

If I’m installing a high-current accessory in any vehicle with a frame under it, I always use the frame for the return path for said accessory. As shown, white lithium grease can help to prevent such connections from corroding and/or rusting over time.

 

Go big or go home, right? An audio system with thousands of watts of power, such as this one, requires substantial upgrades to a charging system to supply it with power.

Go big or go home, right? An audio system with thousands of watts of power, such as this one, requires substantial upgrades to a charging system to supply it with power.

 

Both the 1/0 AWG cable from the battery (-) and the 4 AWG cable from the case of the alternator are tied to the front sub-frame. This common connection point provides a low-resistance return path for the power-hungry amplifiers in the trunk.

Both the 1/0 AWG cable from the battery (-) and the 4 AWG cable from the case of the alternator are tied to the front sub-frame. This common connection point provides a low-resistance return path for the power-hungry amplifiers in the trunk.

 

All audio system electronics in the trunk are tied to a ground distribution block mounted in the driver’s side of the trunk. In turn, this block is tied to the rear sub-frame on the driver’s side (same side as the battery and alternator ground connections up front) with 1/0 AWG cable.

All audio system electronics in the trunk are tied to a ground distribution block mounted in the driver’s side of the trunk. In turn, this block is tied to the rear sub-frame on the driver’s side (same side as the battery and alternator ground connections up front) with 1/0 AWG cable.

 

As I use a 1/0 AWG lead between the battery and audio amplifiers in the Mustang, follow along with the upgrades I did to the return path to ensure proper operation:

  • Choose a connection point on the side of the frame closest to the vehicle’s battery.
  • Connect the same size cable from the battery (-) to the frame as the main power cable feeding your accessory—in this case that would be 1/0 AWG.
  • Connect the same size cable from the case of the alternator as the alternator’s charge lead to the frame at the same spot you connected the battery (-) to—in this case, that would be 4 AWG.
  • In the rear of the vehicle, connect the same size cable as the main power lead to the same side of the frame to your accessories—1/0 AWG again.

Make sure to clean the paint or undercoatingwith a grinder or rotary tool to get a good electrical connection. I like to use star washers to get a good bite into the metal. Finally, use white lithium grease to protect these connections from rusting or corroding. This is just good practice to ensure good solid electrical connections for many years to come.

Many vehicles have unit-body construction, so they don’t sit on a full frame. In the case of the Mustang, which I used in the above example, it has subframe connectors welded between the front and rear frames, so I chose to use the frame as a return path over the chassis. This is common practice. Even if it didn’t have subframe connectors, I would have still done it this way, as experience has shown that this still offers a lower resistance return path than the chassis alone.

CAUTION: Do not drill holes in the frame of a vehicle, as it can be tempered for strength. Rather, locate a pre-existing bolt and connect your ground wire under it. If no pre-existing bolt is present, then locate a hole in the frame and tap it.

 

MuscleCarB

 

Upgrading the Alternator

If you add a handful of low-cur-rent accessories, the stock alternator on your vehicle should be able to easily power them as it has some reserve capacity built in. How do you know when you’ve exceeded its ability? Simple—with your DMM:

  • Connect it directly to the battery terminals so that you can observe its DC voltage.
  • Have a helper start the engine and turn on your commonly used accessories such as the air conditioning, headlights, radio, defroster, etc.
  • Raise the engine speed to around 2,000 rpm, which is typical when cruising around town or on the highway.

If voltage at the battery is below 13 VDC, then the battery will not receive sufficient charge to be recharged when you’re driving and using these accessories. In addition, if your DMM indicates a voltage drop below 12.6 volts DC (great use for the MIN measuring mode), the battery acts as a buffer, supplying current to the accessories that cannot be replenished by the alternator. This is a recipe for a dead battery—no, it isn’t the battery’s fault and, no, a bigger battery won’t solve the problem!

You need to consider the additional current requirements of the accessories you’ve added and upgrade your alternator and its charge lead accordingly per the directions supplied by the manufacturer of the alternator you choose. In the case of the Mustang, this called for a 200-amp unit from Ohio Generator. A maximum of 4-gauge charge leads is recommended.

Upgrading the Battery

When is a good time to upgrade the battery? Notice that I left it for dead last—ironic, huh? Most folks upgrade the battery first because they have no idea of its real function. I typically upgrade the battery only when I need to.

 

An Ohio Generator 200-amp alternator on the Mustang is a direct replacement for the factory unit. Per their recommendations, the stock charge lead is upgraded with 4 AWG. The 4 AWG silver wire connects the case of the alternator to the front sub-frame, as pictured on page 97. The insulation of these wires has turned black over time from heat due to their proximity to the thermostat housing.

An Ohio Generator 200-amp alternator on the Mustang is a direct replacement for the factory unit. Per their recommendations, the stock charge lead is upgraded with 4 AWG. The 4 AWG silver wire connects the case of the alternator to the front sub-frame, as pictured on page 97. The insulation of these wires has turned black over time from heat due to their proximity to the thermostat housing.

 

A high-quality aftermarket battery typically has lower overall impedance than the OEM unit it’s replacing. Therefore, it can store and release charge more effortlessly than a stock battery. There are many different types of high-quality batteries on the market, the most popular are the AGM (Absorbed glass mat) variety. When replacing or upgrading your battery, this is a good time to take into consideration the reserve capacity or AH rating. Often, you’re limited only by the size of battery that fits in the stock location.

 

Replacing a Battery

As a battery ages, it can become increasingly difficult for the alternator to charge. In some cases, it can develop a dead cell, which causes the alternator to work overtime trying to charge. If you think your battery is in need of replacing, you can make a more educated guess using the following steps:

Step 1:

Allow the vehicle to sit overnight.

Step 2:

With the Ignition switch in the off position, turn the headlights on for 30 seconds to bleed off any surface charge that may be present.

Step 3:

Turn the headlights off and connect your DMM across the battery to measure its voltage.

Step 4:

If you measure voltage below 12.4 VDC, let the battery sit for an hour or two and take a second measurement.

Step 5:

If you measure closer to 12 VDC on the second go around, it’s safe to assume that your battery has seen better days and should be replaced.

Before yanking it out, you can try some of the things in the battery maintenance sidebar in an effort to bring it back to life.

Protecting Your Work

Adding a circuit of any type to a vehicle involves further considerations. Specifically, they are:

  • Fusing.
  • Suitable fuse locations.
  • Routing of the wiring.
  • Protection for the wiring itself.
  • Anchoring the wiring.

This is the area most neglected by the do-it-yourselfer. Incidentally, over-look this part and your vehicle could be the next one on the side of the highway burning. (To this day, when I see that, it makes my stomach turn.)

Fusing

When adding an accessory that draws high enough current to have to be connected to the vehicle’s battery directly, this wire has to be fused. This fuse value should be chosen according to:

  • The manufacturer’s specifications of the accessory(s).
  • The current capability of the wire.

39

 

Again, there is a science here to work by and that science is math. The chart on page 100 shows the cur-rent capability of a gauge of wire versus its length.

Let’s go back to the previous example of the amplifier in my wife’s truck. The amplifier requires a maximum of 60 amps of current to be able to make full output. According to the chart, this is well within the current carrying capabilities of 4-gauge wire over a 20-foot run.

Suitable Fuse Locations

More commonly, when we add a high-current circuit to a vehicle, we connect its power cable to the battery directly. This also necessitates that we fuse this lead within a short distance from the battery to protect it from a short circuit in its run. An example of such a short could be if the vehicle was involved in an accident and the power cable was pinched as a result. If this cable was not fused, it could start a fire, which would quickly turn a bad situation into a very bad situation. Common practice is to fuse a cable within 18 inches of the battery post. I typically install fuses closer than that, but certainly no farther apart.

 

An Ohio Generator 200-amp alternator on the Mustang is a direct replacement for the factory unit. Per their recommendations, the stock charge lead is upgraded with 4 AWG. The 4 AWG silver wire connects the case of the alternator to the front sub-frame, as pictured on page 97. The insulation of these wires has turned black over time from heat due to their proximity to the thermostat housing.

An Ohio Generator 200-amp alternator on the Mustang is a direct replacement for the factory unit. Per their recommendations, the stock charge lead is upgraded with 4 AWG. The 4 AWG silver wire connects the case of the alternator to the front sub-frame, as pictured on page 97. The insulation of these wires has turned black over time from heat due to their proximity to the thermostat housing.

 

No place under the hood of your car to mount a fuse holder? Make one. Pictured here is a simple fuse holder mount that I made with 3/8-inch-thick plastic on a band saw. This took minutes, mounts to the overflow reservoir support, and provides a flat mounting location for the fuse holder itself.

No place under the hood of your car to mount a fuse holder? Make one. Pictured here is a simple fuse holder mount that I made with 3/8-inch-thick plastic on a band saw. This took minutes, mounts to the overflow reservoir support, and provides a flat mounting location for the fuse holder itself.

 

A second consideration is where to mount the fuse holder under the hood of a vehicle so that it is within 18 inches of the battery and solidly mounted. You just have to look under the hood of any new car to notice that real estate is at a premium. This is the case in both the Nissan Frontier and the Mustang GT. Fortunately, it is simple enough to make a mounting bracket from metal or plastic, mount this to the vehicle, then mount the fuse holder to this.

It is not acceptable to leave a fuse holder unmounted or “mount” it to a wire harness with a cable tie. They have provisions for mounting for a reason—use them.

Routing of the Wiring

As I mentioned above, I follow factory wiring harnesses whenever possible. When it’s not possible, I like to route my wiring as high as possible. Whether under the dash or under the hood, keeping your wiring up and out of the way of moving parts or sources of heat pays off in spades. Be aware of hood hinges as they’re up and out of the way with the hood up!

If you have to run wiring in-between metal barriers, such as between the chassis and the door in the doorjamb, then you’re best advised to think about how water travels. If you look closely at the harness installed by the OEM in a door-jamb, the hole in the body is always higher than the hole in the door itself. This allows water to flow down-ward when it rains. If water gets into the door, the door has drain holes in it to accommodate this, whereas the chassis inside the body does not.

Running wiring under the vehicle is totally acceptable and in many cases can be the only way to do it—especially with large-gauge power wiring. Be sure that you cover the wiring with one of the methods out-lined in the next topic and that it is anchored properly. Inside or along-side the frame rail is an excellent location to run such wiring.

Protection for the Wiring Itself

There are many different types of wiring looms and sheathing available to protect the new wiring. In addition, this gives your work a clean and professional look. There are a seemingly endless selection nowadays; this book covers the three most common.

 

Split loom tubing is quite handy indeed. It’s easy to install, looks justlike what most OEM’s use, and comes in sizes from 1/8- to 2-inch diameters.

Split loom tubing is quite handy indeed. It’s easy to install, looks justlike what most OEM’s use, and comes in sizes from 1/8- to 2-inch diameters.

 

Split Loom Tubing: The most popular type of covering is split loom tubing and it is available in diameters ranging from 1/4 inch to more than 1 inch. This stuff is easy to slide over wiring, as it has a slit in one side.

Making Split Loom Tubing

I like to go the extra mile with split loom tubing and finish it off like the OEMs do. Here’s how to do that with a wire terminated with a crimp connector like a ring terminal:

Step 1:

43Cut the loom so that it is about 1/4 inch shorter than the insulation of the ring terminal.

 
 

Step 2:

44Wrap Super 33+ Tape around the insulation of the ring terminal a turn and a half to two turns.

 
 
 
 

Step 3:

45Slide the loom over the ring terminal so that the tape comes through the loom at the slice.

 
 
 
 
 
 

Step 4:

46Continue wrapping the tape around the terminal and loom and go down the loom about an inch past the terminal, tear the tape and finish the wrap.

 
 
 
 

Heat Shrink Tubing: As stated in Chapter 3, this tubing is good to have on hand. I like to use it in conjunction with split loom tubing to provide an even better look than you can get with the method I showed you above. Just cut a piece about 2 inches long and heat it over the end of your split loom for a really great-looking finish.

 

Heat shrinking the ends of your split loom tubing is easy. You need to be sure to put it on the tubing first if you plan to terminate the cable with a big ring terminal like the one here. While heat shrink tubing takes a little extra time, the looks are sure worth it!

Heat shrinking the ends of your split loom tubing is easy. You need to be sure to put it on the tubing first if you plan to terminate the cable with a big ring terminal like the one here. While heat shrink tubing takes a little extra time, the looks are sure worth it!

 

lf wire must be routed near sources of very high heat (such as the exhaust), consider using high-temperature sheathing for the wiring or looms of wiring. When I use this stuff, I typically loom my wiring as normal, then I slide the sheathing over the loom and heat shrink it to the loom to give it a nice finished look.

lf wire must be routed near sources of very high heat (such as the exhaust), consider using high-temperature sheathing for the wiring or looms of wiring. When I use this stuff, I typically loom my wiring as normal, then I slide the sheathing over the loom and heat shrink it to the loom to give it a nice finished look.

 

High-Temperature Sheathing: When you have to run cables or wiring near areas of extreme heat, like the Hooker Super Comp headers in my Olds, you’d be well advised to cover it with this stuff. It’s readily available at your local performance parts shop.

Consider the problem of a heat-soaked starter. We’ve all been there, and me just recently! You pull into the cruise, let your car sit for a while, then go to start it to leave and nada. No matter how hard you try, the starter just won’t do anything. This meant that I had to wait another hour or so for it to cool down before I could leave—a favorite with the wife that just spent the last hour humoring me, looking at the same cars I saw the week before.

What really causes this? Is it a bad starter? In the case of the Oldsmobile, it was the following:

  • The solenoid for the starter motor is on the top of the starter, so it is extremely close to the headers.
  • The heat from the wrapped 21/8-inch internal-diameter, thin-walled headers caused the copper within the solenoid trigger wire to become very hot after the car sat for a while, limiting its ability to pass current.
  • The wiring going to the solenoid trigger couldn’t pass the current the solenoid required of it when subjected to this heat.
  • The wiring to the solenoid trigger was 16 AWG (one of the few things that I left from the last guy’s work)—the bare minimum to trigger the solenoid.

 

Here is a great example of where and when to use high-temperature sheathing. I used it to protect the wiring for the trans-temp gauge, the trans-brake, and the starter in my Olds as all these cables pass within close proximity of the passenger-side header.

Here is a great example of where and when to use high-temperature sheathing. I used it to protect the wiring for the trans-temp gauge, the trans-brake, and the starter in my Olds as all these cables pass within close proximity of the passenger-side header.

 

High resistance plus high heat is not a good combination. Fortunately, the solution was simple. I used the 16-gauge wire to trigger a Bosch relay mounted under the dash, which feeds 10-gauge wiring to the solenoid trigger input. As I installed an extra fuse panel in the Olds for circuit expansions, the source of power was easy. In addition, I sheathed this wire to the solenoid with high-temperature covering.

Problem solved! I’ve driven the vehicle for several months now and never had so much as a hesitation when starting it. I should have looked up the current requirement of the solenoid trigger wire versus assuming that it was like a Ford solenoid

Anchoring the Wiring

If this sounds so obvious, why then do I see so many examples of how not to do this when I’m looking under the hood or the dash of a car at the local gathering? Wiring is the one task that most people just wanna get done; once they get the circuit working, they tend to leave it that way. Finishing the wiring is always on a car guy’s list—the list that never seems to get done because the turbo needs to be bigger, the suspension needs tweaking, etc.

When it comes to safety, this is one of the most important aspects of any wiring job. Second only to fusing, properly securing any added wiring is a really important thing to finish. Wiring hanging down below the dash is simply unacceptable as it can get tangled in the pedals, steering, etc. Wiring under the hood that isn’t anchored can quickly find its way to the exhaust manifold or any number of other hot or moving parts. Even worse is wiring that isn’t fused or anchored—this is simply a vehicle fire waiting to happen.

 

Cable ties keep your cable runs neat and tidy and out of the way of moving parts. Also shown is the connection from the alternator case and the return path for all the accessories in the front clip of the Olds. Note that I tapped an existing hole in the frame and used a 5/16–18 bolt for this connection.

Cable ties keep your cable runs neat and tidy and out of the way of moving parts. Also shown is the connection from the alternator case and the return path for all the accessories in the front clip of the Olds. Note that I tapped an existing hole in the frame and used a 5/16–18 bolt for this connection.

 

Tie downs are great to anchor wiring and looms of wiring to a vehicles chassis or frame. The one used here has a rubber lining within a metal clamp assembly. Nice thing about these is that your local home improvement store typically stocks them up to about 2 inches in diameter.

Tie downs are great to anchor wiring and looms of wiring to a vehicles chassis or frame. The one used here has a rubber lining within a metal clamp assembly. Nice thing about these is that your local home improvement store typically stocks them up to about 2 inches in diameter.

 

Again, this is easy stuff. The most common methods of anchoring are by use of cable ties and tie downs.

Cable Ties: These are available in both natural and black and in all different lengths up to about 3 feet.

After I tie them and cut off the excess, I like to rotate the tie so that you can’t see the cut end. This gives my work a really clean and professional look.

Do not use cable ties to tie anything to rubber vacuum lines or hard air-conditioning lines under the hood of the vehicle. Cable ties can damage these lines.

Tie Downs: These are available in both plastic and metal with rubber linings. You can get them at your local hardware or home supply store in bulk and save a few bucks over buying them in pairs at the auto parts supply store. These are handy for securing large-gauge cables or harnesses, especially when you have to run them under the vehicle.

 

Written by Tony Candela and Posted with Permission of CarTechBooks

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