Muscle Car Interior Restoration: Electrical & Wiring Guide

If you’re going to take out your dashboard in this quest for the ultimate interior restoration, you need to address your electrical system— yet another restoration topic that causes most guys to groan. Electrical systems often seem counterintuitive and often frustrate us to no end. As time went on, they became more complex, they added more buzzers and chimes and features, and they became more troublesome to troubleshoot and repair.


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But if you leave all that wiring alone and don’t at least inspect it now, while you have better access to it, then often down the road—maybe months, maybe years—something in that bundle of wires will go poof. Remember, mice will chew on electrical wires just as soon as they’ll chew on anything else; their incisors never stop growing, so they need to chew on something, anything, to keep their incisors in check, and wiring works to that purpose. By chewing through the plastic insulation around the wires, they’ve then created a big opportunity for a shorted circuit.

Of course, mice aren’t the only culprits of electrical trouble. Loose wires, along with wires that chafe and fray on ungrommeted or otherwise unprotected metal surfaces, can short. Corrosion in connectors can cause bad grounds, interrupted circuits, or (most bedeviling) intermittently interrupted circuits. And 40-year-old fusible links give up the ghost every now and then.

The end result of releasing the smoke from the wires could simply cause your muscle car to die by the side of the road, or it could catastrophically send your muscle car up in flames. Do you want to take that chance just because you neglected to check your wiring?

And besides, it could be worse: You could be working on a British car’s Lucas electrical system.

Electrical Theory and Components

Entire books have been written exclusively on electrical theory and on wiring automobiles, so to cover those topics in their entirety isn’t the aim here. But, much like interiors in general, many gearheads leave all their wiring jobs up to the professionals simply because they refuse to take the time to learn some basics about all those brightly colored wires under their dash.

To understand wiring, you need to understand the basic circuit. And to do that, it often helps to think about electricity in terms of plumbing. Wires are your pipes, and through them, respectively, flow both electricity and water. A battery is similar to a reservoir of water, with the positive terminal at the spigot end and the negative terminal at the fill point; your alternator is similar to a pump that keeps filling the reservoir. Because it’d be pointless to have the water filling and emptying in an ongoing cycle, let’s introduce a component: In our plumbing circuit it might be a water wheel, but in our electrical circuit it might be a light bulb. There, now our circuit has a reason for existing.

Multitesters are available with either a digital screen or a dial. When troubleshooting your muscle car’s electrical system, the two most common functions on the multitester that you’ll want to use are the voltage (set your dial to 20V, as we did here) and the resistance (set your dial to one of the ohm ranges, depending on the amount of resistance you expect to find).

Multitesters are available with either a digital screen or a dial. When troubleshooting your muscle car’s electrical system, the two most common functions on the multitester that you’ll want to use are the voltage (set your dial to 20V, as we did here) and the resistance (set your dial to one of the ohm ranges, depending on the amount of resistance you expect to find).

Two important measurements in an electrical circuit—voltage and amperage—are roughly equivalent to the pressure and flow rate in a plumbed system. An electrical system with higher voltage simply has greater potential or force of electricity, while one rated with higher amperage just has a greater volume of electricity. This is why you can power a 12-volt system with a 6-volt battery—you’ll just get a weak result. But you can’t power a 6-volt system with a 12-volt battery—twice the push means you’ll start overloading components in no time.

Voltage and amperage are obviously interconnected, and the relationship between the two depends on the resistance in the circuit. Ohm’s Law expressed that relationship as V=I x R, where V stands for voltage, I stands for current or amperage, and R stands for resistance. You don’t have to memorize the formula as you did back in highschool physics class, but for our purposes, it does illustrate how, when the voltage remains the same and resistance increases, current naturally decreases.

By the way, this is all relevant mostly to direct-current (DC) circuits rather than alternating-current (AC) circuits. That’s good, because your muscle car uses DC circuits. And, of course, by the beginning of the muscle car era, every manufacturer had switched to a 12-volt system. You’re only likely to encounter 6-volt systems in cars older than the mid- 1950s, and you’re only likely to encounter 24-volt systems in military vehicles.

So in our basic circuit, we have the battery, we have the wires to conduct the flow of electricity, and we have the light bulb. Unlike pipes, however, when wires are left disconnected, they don’t just let the electricity spill out. Instead, the flow of electricity stops and nothing happens—you have a dead circuit. The same thing happens when you introduce a switch to the circuit. When turned off, the switch introduces a break in the current and the circuit dies; the light bulb goes off. When turned on, the switch allows the current to flow once again, and the light bulb lights up. The same thing also happens when the grounds in your circuits become too corroded and no longer conduct electricity, except that happens without your control, which is why it’s important to check and clean all exposed grounds and other connectors.

Aside from the battery, switches, and light bulbs (or fans, or power window motors, or any other device that uses electricity for a specific purpose), you’re likely to encounter a couple other basic components: the relay and the fuse.

The relay is essentially a remoteoperated switch. Applying an electrical circuit to a relay (usually with a switch) causes an electromagnet in the relay to close or open a second, separate circuit. This is done for a variety of reasons, usually to provide the shortest physical path possible between two points, because excessive wire in a circuit results in excessive resistance.

The fuse is simply a piece of metal designed to blow when current in that circuit exceeds a predetermined amperage. Fusible links often performed the same task in vehicles from the muscle car era, though they relied on sections of wires in a circuit designed to melt above a certain amperage. The advantage of a fuse over a fusible link is that the former can be easily inspected and replaced, while the latter is hard to locate and can pose a fire hazard if it melts too violently. Fusible links were really used to protect the car’s wiring from overloads in case of a violent wreck that pinched the wiring. Consider replacing your fusible links with fuses of the same rating, even if the fusible links have yet to blow.

As long as your muscle car’s electrical system has remained untouched, the most common cause for a blown fuse is a short circuit, which happens when the plastic insulation around a wire has been compromised and the wire touches a nearby ground. You’ll keep blowing fuses until you’ve addressed that short circuit. To find the short circuit, you’ll likely want to use a multimeter, also called a multitester, which can measure voltage, amperage, and resistance. To use a multitester, simply turn the dial to the scale you want to measure, then use the two probes attached to the multitester to form a temporary circuit.

Once you’ve located the source of the short circuit (and hopefully addressed the cause of the compromised wiring), it’s time to repair the wire itself. However, diagnosing and resolving the full range of potential electrical problems is outside the scope of this book. If your particular restoration project requires extensive electrical work, I recommend Automotive Wiring and Electrical Systems by Tony Candela.

Wiring Repair

What very few people who work on cars nowadays seem to understand is that wire nuts are not permanent solutions for splicing a wire, at least not in an automobile. In your house, it’s fine to twist up a pair of stripped wires and toss a wire nut on them because your house isn’t constantly moving and vibrating. Your car, however, does move and vibrate, which is one of many reasons why you shouldn’t shop for car supplies at your local homeimprovement warehouse.

Wire nuts are a decent temporary solution. If you’re on the road without access to a soldering iron and just need to go home, fine. But once you get there, you need to come up with a more permanent fix for your wires, which means you’ll want to solder them together.

One quick note to keep in mind before undertaking any electrical work on your car: Disconnect the battery first. If you neglect or otherwise forget to do so, a shock from your car’s 12-volt DC electrical system might not be enough to kill you, but it sure could make things a little uncomfortable for you, and the real danger in leaving the battery connected is to your car’s components— relays, fuses, bulbs—none of them much appreciate unexpected jolts of electricity. A battery disconnect switch can take the hassle out of repeatedly removing and replacing battery cables from battery posts, but is also useful in preventing battery drain when your muscle car sits out in winter, and in preventing thefts.

The drawback to soldering wires is that the solder makes them stiff at the joint and, thus, more prone to snapping than an uninterrupted piece of wiring. So you’ll want to make the joint as strong as possible with as little solder as possible. One of the strongest methods of wire splicing is to strip about 1 to 11 ⁄2 inches of insulation from the wire on either side of the splice. For thickergauge wire, strip more, and for thinner gauge wire, strip less. Only use a quality wire stripper designed for multiple-gauge wires; stripping wire with a knife or with your teeth may nick the strands of wire underneath, causing a mechanical weakness in the wire.

Wiring Repair

Step-1: Wiring Repair

1For wire repair, you need a soldering iron, a roll of solder, a wire stripper (which usually has an integrated wire cutter, though we often prefer to use side cutters to snip wires), and either heat shrink tubing or electrical tape. For simple repairs, don’t concern yourself with the many different types of soldering irons out there—they all work well.





Step-2: Wiring Repair

2The strongest wire splicing method we’ve come across starts with stripping about 1 inch of insulation from the wires, then bending the ends of the wires back on themselves to form a couple of hooks. Note that the copper strands remain shiny and uncorroded; dirty, corroded strands of wire should be replaced.




Step-3: Wiring Repair

3Next, hook each wire into the other and twist the hooked ends of the wires back over themselves. Though the wires may flop around at this point, they’re very difficult to pull apart. Note how little bulk this repair creates.





Step-4: Wiring Repair

4Here’s where you could really use a third hand sometimes. Apply the tip of the soldering iron to the joint between the two wires and, after a minute or so, the wires will be hot enough to allow the solder to wick into the strands.





Step-5: Wiring Repair

5A good solder joint shouldn’t have any big blobs of solder— those come with applying the solder directly to the soldering iron—and should prevent the joint from wiggling, which could lead to an intermittent connection.





Step-6: Wiring Repair

6After letting the solder joint cool, slip the heat shrink over the joint so that it overlaps the insulation on both sides. Logistically, you should slip the heat shrink over one of the wires before making the connection. A bit of directed heat from a butane lighter or from a heat gun will seal the tubing to the connection.




Step-7: Wiring Repair

7With just enough of the wire stripped for the terminal, we selected the right gauge of female spade terminal, then removed the plastic boot from the terminal. Plastic boots don’t seal against the elements as well as a small section of heat shrink or a small length of electrical tape, so it’s best to remove the boots from the terminals.





Step-8: Wiring Repair

8Note that we crimped the terminal so the seam folds in, and thus grips the wire strands for a stronger connection. Also note the tiny tab at the end of the copper strands of the wire. The tab limits how far you can push the wire into the terminal, to avoid the wire interfering with the terminal’s connection.




Step-9: Wiring Repair

9Next, we secured the crimp with a dab of solder just to be sure that it won’t work loose over time. We’ll follow the crimp with a short length of heat shrink and a dab of dielectric grease to prevent corrosion of the terminal.




At this point consider the amount of strain that the wire will be under. You don’t want to leave the wire shorter after your repair; it will become tighter and more prone to snapping. But you don’t want to give it too much slack either, as the wire may come into contact with a heat source or spinning blades, or it may be pinched somewhere else. If you find your wire is too short, cut a scrap piece of wire of the same gauge and splice it into your repair to extend the wire. If you find it is too long, consider incorporating what professional electricians call a service loop elsewhere in the circuit.

Cut an appropriate length of the appropriate gauge of heat shrink tubing and slip it over one of the wires at this point. Then bend the strands of both wires back over themselves in a gentle curve, back no farther than the insulation. You’re essentially making two hooks—like two pieces of Velcro—and you’re going to hook them together in the same way. After hooking the wires together, twist the strands of the wires back around themselves.

With the strands twisted tightly, try pulling the two wires apart. This joint requires a good yank (more than you’d see in typical automotive use) to separate the two wires now. Add in the benefit of a sleek, less bulky repair, and it’s about as good as you’re going to find for a joint between two wires. You could actually slip the heat shrink tubing over the joint now and be done, but adding a bit of solder will secure the connection. The soldered area won’t have the same level of tensile strength or electrical conductivity as an uninterrupted strand of wire, but using higher quality solder—that is, a solder with greater concentrations of tin over lead and one with fewer impurities—will minimize the losses in strength and conductivity.

So, with your soldering iron warmed up, clean off the tip with a damp sponge and apply the heated tip to the wire joint. Give it a second or two to heat up the strands of the wires, then apply the solder to the hot wires—not to the tip of the soldering iron. As long as the wires are hot enough, the solder will flow between the strands by capillary action and it won’t be necessary to move the soldering iron. Apply just enough solder to fill the joint; you don’t want to see big blobs of excess solder anywhere near the joint.

Remove the soldering iron and let the joint cool before slipping the heat shrink tubing over the joint. Whether you use a lighter or a heat gun, start heating the shrink tubing at the center and work your way out toward the ends; doing so prevents pockets of air from getting trapped. The heat shrink tubing should conform tightly to the wire joint—if it’s too loose, you used a piece of tubing that was too large— and its ends should overlap and seal against the wire insulation.

Of course, not all wiring repairs take place in the middle of a wire (where the above method works the best). Many take place at the end of a wire, where a terminal has corroded or gone missing. The first order of business then is to find an appropriate replacement terminal. Your corner auto parts store should have a good selection of automotivegrade terminals. Pick up a large variety pack, even if you only need one terminal out of the pack—it’s a pain to have to keep venturing out to the store for one or two small terminals. If the corner auto parts store doesn’t have a good selection of terminals, you can find high-quality terminals by browsing the catalogs of industrial supply companies such as Terminal Supply Co. or McMaster-Carr.

Most parts-store terminals, however, have cheap plastic boots on one end, color coded to the gauge range of wire that the connector works best with. They’re a good idea for fieldwork, but for a permanent solution, it’s best to strip off that boot, exposing the crimp end of the terminal, and use a short section of heat shrink tubing in its place. Follow this procedure:

  • Strip a short section of the wire— just enough to fit in the crimp section of the terminal—and insert it in the terminal.
  • Place the terminal so the seam of the crimp area will fold in on the wire instead of pucker out away from the wire.
  • Using your crimping tool, insert the crimp end of the terminal in the appropriate slot for the gauge of the wire, then crimp the terminal two or three times, depending on the length of the crimp section.
  • For an extra-strong connection, solder the crimped area.
  • Cover the crimp with heat shrink tubing.
  • Coat the terminal with dielectric grease to prevent further corrosion.

What if you don’t want to use heat shrink tubing? Well, nothing compares to properly applied heat shrink tubing when it comes to preventing corrosion of the wires exposed in your repair, but it is rather pricey, and if you’re making numerous splices, those costs can add up quickly. Garden-variety electrical tape, stretched tight, can seal splices just as well. However, the glue in electrical tape often oozes out under high temperatures and creates a sticky mess, so use electrical tape sparingly. If wrapping an entire wiring harness, instead of electrical tape, use a product such as Eastwood’s Tommy Tape or 3M’s self-vulcanizing tape, which is not adhesive backed, but instead clings to itself when lightly stretched.

Finally, when using clamps to secure a wiring harness, try to avoid uninsulated metal clamps, not necessarily because they conduct electricity, but because their bare edges can chafe away the insulation from wires over time, allowing the wire to short to ground through the clamp. Instead, use clamps that have a rubber pad that covers the edges of the clamp. For the same reason, make sure every wire that passes through the firewall or other piece of sheetmetal has a grommet to pass through, and thus prevent abrasion and unintentional grounding.

If the wiring harness is missing, extensively damaged, or if its repair requires too much effort, several companies offer partial and complete reproduction-wiring harnesses. Thanks to the burgeoning street rod aftermarket, other companies offer complete custom harnesses designed specifically for your muscle car and for its particular electric requirements.

Radio Upgrades

Looking back on the option sheets of most muscle cars from the 1960s and 1970s, one option tended to cost much more than all the other options. Big-block engines? Nah, just a couple hundred dollars here and there for the less exotic ones. Air conditioning? Pricey, but still not a bank breaker. Instead, the top-end stereo options usually topped the lists at around $500 and could include all the latest technology: FM! Balance! Station seeking! Pushbutton channel selection!

And back then, just as they do today, teenage boys spent as much, if not more, on their tunes as they did on their engines. Maybe they didn’t always buy the top-end stereo, however. And they’d certainly freak if they witnessed the audio technology we have today: multichannel, highwattage sound systems able to play a near-endless stream of music from satellite radio and MP3 players. Internet radio piped through your car stereo has even become a possibility within the last year.

Over the decades, a number of would-be stereophiles have attempted to upgrade the stock sound systems in their muscle cars, and in that process, they probably became one of the main causes of door panel, package tray, and faceplate replacement in muscle cars today. On the plus side, many of those parts are reproduced today, and I cover their replacement in other chapters of this book; I even cover plastic repair in Chapter 6, for those of you with butchered radio faceplates. However, it also means that your muscle car’s original radio is long gone, and you’re going to want to find another one.

Fortunately, another advance in technology over the last decade now allows you to stuff all that modern audio wizardry into the simple, little, one-speaker radios and two-speaker stereos that came with your muscle car, all while leaving those radios and stereos looking stock and without any extra controls added. It’ll cost a little bit more than a typical stereo restoration back to totally stock innards, but it’ll be worth it when you tell your kids they can plug their iPods into your Chevelle.

The downside of the process is that it’s difficult to do yourself. Even if you’re handy with a soldering iron and surface-mount circuit boards, you’d still have to find a digital conversion kit, which is not sold as a retail item to the general public. Only certified installers can buy the digital conversion kits, so to obtain a conversion, you’ll have to send your radio to an installer.

An alternative is to buy one of the many ready-made digital radios out there that fit into your car’s dash without cutting the dash apart. You get the same results as a digitally converted radio, but many of these digital radios have digital displays instead of a tuner dial on the face. A digitally converted radio will have the exact same faceplate and dial that the radio came with from the factory.

The digital conversion starts with an inspection and disassembly of the radio. The chassis of the radio, stamped out of sheetmetal, is usually used to ground circuits, so several wires are likely soldered directly to the chassis and will need to be de-soldered or clipped. Also, because the radio provides a flat, hidden, horizontal surface, a common source of damage to a radio comes from mice, which often find the top of a radio a good place to hang out and nest. So while disassembling the radio, wear a dust mask until the dust and debris inside the radio has been removed.

Because the digital conversion kit uses the existing mechanical workings of the radio, but replaces most of the electronics, check all of the mechanisms, including the knobs, the push buttons, and any selector switches, to make sure they work properly. If they don’t, the mechanisms will need to be repaired or replaced. For example, radios are often damaged during shipping—or even while in the car—when the knobs are struck from the front and the force of the impact shatters the switches and potentiometers behind the knobs.

Here’s our traditional before picture of the radio that we’re converting to digital. It’s a typical mid- 1960s Chevrolet AM/FM push-button radio with only a tone dial and no provision for balance or fade control. We’ll add the latter two, along with four-channel sound and the ability to play external devices, such as CD or MP3 players.

Here’s our traditional before picture of the radio that we’re converting to digital. It’s a typical mid- 1960s Chevrolet AM/FM push-button radio with only a tone dial and no provision for balance or fade control. We’ll add the latter two, along with four-channel sound and the ability to play external devices, such as CD or MP3 players.

However, in most cases, any damage to a radio is in the electronics and is done over time as the components, such as the capacitors and transistors, either decay from use or fail from voltage spikes. Returning to our example of the knobs, if you were to take apart the potentiometer that the knob turns, you’ll usually find a thin, round circuit board with a copper trace embedded into it. With repeated use over the decades, the copper trace starts to break apart, forming a poor connection, and can only be realistically repaired by replacing that little component. If the entire potentiometer can be replaced, it’s often quicker and easier to do just that.

Fortunately, most of the electronics inside a stock 1960s radio are removed for the digital conversion. All that really needs to remain are the contacts on the switches and potentiometers behind the tuning and volume knobs, and the tuner itself, which looks like a row of either three or six conjoined cylinders—three for AM and six (actually two banks of three) for FM. In most muscle cars, technically the tuner is called a variable inductance transducer, and what it does is take the mechanical input (from your fingers turning the tuner knob) and convert it into an electrical output signal. If you leave the tuner mechanism hooked up, you can watch a series of pistons slide in and out of the cylinders as you turn the tuner knob to go up and down the dial. Combined with the antenna, the signal that the transducer outputs then becomes translated into something that your ears recognize by all the electronic guts of the radio that are about to be replaced.

Radio Upgrades

Step-1: Radio Upgrades

1Disassembly begins with the top plate. The 1960s solid-state electronics were actually rather advanced for their day—no tubes and the ability to pick up both bands of radio. Nearly all of the circuitry, however, will be scrapped for the digital conversion.





Step-2: Radio Upgrades

2If you take apart any potentiometer in a volume, tone, balance, or fade knob, you’ll find a disc like this one, which is a very simple circuit board with a variable resistor embedded into it. A malfunctioning volume control can, in most cases, be traced to this disc, which is easily replaced.




Step-3: Radio Upgrades

3While the radio is apart, the chassis is sandblasted clean, then the individual chassis parts are sprayed with Rust-Oleum’s Hammertone paint. Note that we only sprayed the outside of the chassis parts; the insides will remain bare metal to serve as grounding points for the new electronics.


Step-4: Radio Upgrades

4The heart of the digital conversion is a much smaller circuit board with attached heat sink, and a spaghetti of wires. The pre-terminated wires go to the speakers, while the rest attaches to the radio’s existing controls.




Step-5: Radio Upgrades

5The tuning mechanism of the existing radio will remain with the converted radio. All these mechanisms are checked for correct operation and repaired if necessary. The six horizontal cylinders are the actual tuner that figures out what frequency you’re listening to, based on the physical position of the smaller rods inside the cylinders. An AM tuner, with just three cylinders, is on the left for comparison.


Step-6: Radio Upgrades

6All of the radio’s original components to be reused are laid out, including the cleaned and polished faceplate and the original volume/tone knob. They will be inspected, and if necessary, repaired.




Step-7: Radio Upgrades

7Reassembly begins by mounting the tuning mechanism to the chassis and the faceplate. The device attached to the spiral gear on the right side of the tuner mechanism adjusts the operation of the push buttons and can be tricky to repair



Step-8: Radio Upgrades

8It may seem rather simplistic, but this string, when attached to the slider on the faceplate, pulls the FM dial into view when the FM band is selected. A separate switch, connected to the slider by a short rod, electronically chooses the band and will be connected to the digital conversion kit.




Step-9: Radio Upgrades

9The pull string is attached to the slider and the polished faceplate is screwed to the chassis. Note the stalk of the tuner control on the right and how its nut is tightened against the chassis. These nuts are meant to remain tightened against the chassis, while a second set of nuts is used for the actual installation of the radio in the car.



Step-10: Radio Upgrades

10The top and bottom plates of the chassis are left off for now, to install the digital conversion kit. The knobs will go back on the tuner and volume controls to ensure that those operate smoothly. The circuit board above the tuner knob is the AM/FM switch that will connect to the digital conversion kit.




Step-11: Radio Upgrades

11The circuit board behind the tuner cylinders will eventually connect to the digital conversion kit as well, but most of it is no longer necessary and will interfere with the chosen mounting location of the conversion kit. Because of that, we took a rotary tool and carved out the interfering section of the circuit board.


Step-12: Radio Upgrades

12Though some radios of the 1960s and 1970s offer limited space for the digital conversion kit and require more-creative mounting methods, this one fit rather well after trimming. The heat sink will mount directly to the chassis using holes already drilled and threaded in the heat sink.



Step-13: Radio Upgrades

13We used a second matching heat sink to locate the holes we needed to drill in the chassis. This method of locating the holes takes all the guesswork out of the process. It can be done with a paper template, just as easily




Step-14: Radio Upgrades

14With the locations for the holes marked with a center punch, they can be drilled out. Though we had plenty of room inside the chassis, we still drilled cautiously and slowly to avoid unintentional damage.




Step-15: Radio Upgrades

15Thermal grease applied to the side of the heat sink facing the radio chassis helps transfer heat away from sensitive electronics and to the chassis. Though heat isn’t much of a worry at normal volumes, heading toward the maximum 45-watt output of each channel will generate enough heat to warrant heat dissipation measures.






Step-16: Radio Upgrades

16The heat sink is aluminum and thus doesn’t act as a ground, so all the grounding for the digital conversion kit goes through one wire to the radio’s original ground. Not believing that one wire was a sufficient ground, we soldered a short length of wire from the conversion kit’s circuit board straight to the chassis.




Step-17: Radio Upgrades

17The connections can now be made, starting with the blue and white wires, which provide the signal from the tuner to the conversion kit. Also note the bare wire soldered from the conversion kit to the tuning mechanism. Besides providing another ground for the conversion kit, it also acts as a brace at the normally unsupported end of the conversion kit’s circuit board.




Step-18: Radio Upgrades

18We then made connections from the digital conversion kit to the radio’s original volume and tone knob. We were careful to get the polarity correct on the volume knob in particular. This particular knob also functions as the power switch, so reversing the polarity will cause the radio to jump to full volume instead of low volume immediately after switching it on.





Step-19: Radio Upgrades

19A short length of coaxial cable connects the digital conversion kit to the radio’s original antenna connector. The car’s original antenna remains the same and doesn’t need to be changed.



Step-20: Radio Upgrades

20A pair of RCA jacks, available at any electronics store and used to hook up external music devices, were mounted to the back of the chassis. Fortunately, this chassis had several holes of the right diameter for the RCA jacks. The gray and white wires connect the RCA jacks to the digital conversion board.




Step-21: Radio Upgrades

21Remaining connections include those for the AM/FM switch and for the 12-volt power, the latter of which is done using the radio’s original power feed. The light bulb that illuminates the dial mounts to the top plate of this particular radio, so it’s left dangling for now.





Step-22: Radio Upgrades

22We pulled the speaker wires through the back of the chassis and connected them to the harness supplied with the digital conversion kit. In lieu of a grommet to prevent chafing on the hole in the chassis, we wrapped the wires in electrical tape at that point and used a plastic clamp to secure them to the outside of the chassis.





Step-23: Radio Upgrades

23Before reassembling the converted radio, we tested it to ensure that we made all the right connections and then programmed it to learn both AM and FM bands. (The kits come unprogrammed in case somebody installs one in a Europe-bound car.)




Step-24: Radio Upgrades

24Once the conversion checks out, we finished the reassembly by hooking the light bulb to the top plate and screwing on the top and bottom plates. From the outside, it simply looks like a restored radio, with absolutely no indication that it’ll now play music from any audio device you can conceive, in top quality sound.



With the radio disassembled, the easiest part of the restoration comes next. All the sheetmetal parts of the chassis are sandblasted to remove any rust or debris, then painted in Rust-Oleum’s Hammertone finish. Only the outer surfaces are painted, however; the inner surfaces are left bare to allow the chassis to continue to be used as a grounding path.

The faceplate should now be cleaned and polished with any commonly available plastic polish (see Chapter 2), as should any chrome trim that is visible when the radio is installed in the dashboard. Knobs should be cleaned or replaced with reproductions, if available. As long as the mechanisms inside the radio are still functional, they don’t necessarily need to be taken apart to be cleaned; a few blasts of compressed air, followed by an acid-based wheel cleaner, quickly rinsed away with water and dried with another few blasts of compressed air, should clean out the mechanisms.

Those mechanisms, along with the tuner, faceplate, and knobs, can now be reassembled to the chassis, leaving off the top and bottom plates of the chassis for now.

Next the actual digital conversion kit—a compact circuit board with a large aluminum heat sink and a number of wires coming off it—can be placed in the chassis. Where it goes in the chassis depends on the space available inside each different radio. If not enough space is available, the tuner’s circuit board can be partially trimmed away with a rotary tool—just be careful to leave at least the area on the circuit board with the contacts to which the digital conversion kit will connect. If trimming won’t create enough room for the kit’s circuit board, then as long as space permits outside the chassis itself (but still behind the dash), it may be necessary to fabricate a small sheetmetal box just large enough to house the circuit board, and then secure the box to the radio chassis. Wherever the circuit board is placed, it should not interfere with the mounting location of the stock illuminating lamp. And if you’re going all out, consider an LED bulb for the lamp; this is one bulb you’d hate to replace when it burns out.

The heat sink, which dissipates the heat created when the four channels (at 45 watts each) are cranked up to full volume, is also threaded for a couple screws, so the circuit board should ideally be mounted with the heat sink up against the radio chassis, which will help dissipate the heat away from the heat sink. To take the guesswork out of drilling holes for the two mounting screws on the chassis, make a paper template of the side of the heat sink that will mount up against the chassis and mark the mounting holes on the template. Hold the heat sink up against the chassis and place the paper template on the other side of the chassis, but in the same location as the heat sink. It’s now possible to mark the holes with a scratch awl and then center punch and drill them out. File the holes so the heat sink will sit flush against the chassis, then blow away any shavings or filings. Before actually mounting the heat sink and circuit board, apply a thin layer of thermal grease, available in any hobby or computer store, to the mating surface of the heat sink.

Now comes the tough part that requires the training. A couple specific wires already soldered to the circuit board are soldered at the other end to the tuner, to catch the AM or FM signal. A couple short lengths of wire provide additional grounds from the circuit board to the inside of the chassis. More wires connect the circuit board to the AM/FM switch, to the volume potentiometer, to the tone potentiometer, to the balance potentiometer (if included), and to the antenna connector. Yet another pair of wires connects the circuit board to a pair of RCA jacks, holes for which are drilled in the back of the chassis.

Another wire connects the circuit board to the power source and the power switch. In some radios, the plug for the power and ground wires outside of the radio is separate from the plug for the speakers, and in those cases, the speaker plug can be discarded, but the power plug can remain in place. The ground wire for the power plug is soldered directly to the case, and a capacitor can be used on the power wire to reduce electrical noise.

An optional LED can be connected to the circuit board and hot glued to an unobstructed location behind the faceplate. The LED has three colors: green when the power is on, yellow when the converter picks up an FM stereo station, and red when it picks up an AM station.

Finally, the bundle of wires for the speakers, already connected to the circuit board, is threaded through one of the holes in the back of the chassis. The wires come preterminated and can be snapped into a connector plug; the other half of the plug is supplied with its own matching wires, which can then be spliced into the existing speaker wiring. Make sure the colors of the wires all correspond on either side of the plug. One additional wire in the bundle provides 12-volt power to an external device, such as a CD player or satellite radio receiver.

If you want to keep your muscle car in a state where it can be returned to exact showroom condition, or if you’re otherwise queasy about snipping the perfectly good wires in the factory speaker harness in your car, then it’s a good idea to create an adapter harness to go between the factory speaker harness and the new speaker plug that is supplied in the digital conversion kit. To create an adapter harness, simply locate the radio half of the factory speaker plug (which should have still been attached to your original stereo when you removed it from the dashboard) and cut it from the radio’s original electronics. Splice the wires into the appropriate wires from the speaker side of the conversion kit’s plug. Or, to make matters simpler, use your car’s original speaker plug in place of the digital conversion kit’s speaker plug.

With the speaker wiring taken care of, the digital conversion kit is then programmed to learn the entire FM and AM frequency ranges (it can also be programmed to learn European frequency ranges) and tested. If any of the connections between the circuit board and the radio mechanisms are made backward, the radio could potentially not work, or it could not work as intended. For example, one pair of connections on the volume potentiometer, when made backward, isn’t a big deal unless the power switch is combined with the volume knob, in which case, the radio goes to full volume immediately after it’s switched on.

Here comes the ingenious part of the whole deal. If the radio was originally an AM-only radio, it now receives both AM and FM. To switch between the two bands, turn the radio off, wait five seconds, then turn it back on.

If the radio originally came without balance or fade controls, those are now controlled by the tone knob. To adjust the balance, first tune the radio to a station and adjust the tone, then quickly tune the radio to the bottom of the dial; when the station last playing starts playing again, the tone knob can be used to control the balance. Similarly, to adjust the fade, tune the radio to a station, then quickly tune the radio to the top of the dial; when the station last playing starts playing again, the tone knob can be used to control the fade.

The other genius aspect of the digital conversion is that it doesn’t require a special switch for an external music device. Using the RCA jacks, any such device—from a CD player to a satellite radio receiver to an MP3 player—can be connected to your stereo. (You could theoretically also connect an 8-track or even a record player to your car stereo this way; the latter is not recommended for obvious vibration reasons, while the former is not recommended unless you plan on growing a 1970s moustache and letting your chest hair hang out while wearing bellbottoms and heading to a disco.) The circuit board will automatically recognize a signal coming in through the RCA jacks and switch away from the radio to that input. When the circuit board no longer senses a signal coming from the RCA jacks, it automatically switches back to the radio.

When everything works to satisfaction, the top and bottom plates of the chassis go back on, and the reassembled radio can go back in the dashboard. If you’re planning on using an MP3 player or any other device that you don’t want permanently installed in your muscle car, consider running a cable with RCA jacks on one end and a mini stereo jack on the other end up to your glove box, or any other more easily reached location than the back of the radio. For more permanent external audio devices, consider installing them in the trunk or glove box and run the cable connecting the external device to the radio under the carpet. If you’re planning on using both a permanently installed external audio device and a non-permanent device, an RCA Y-jack can allow two inputs to plug into the stereo at once (just don’t play them both at the same time). Peruse the audio cable aisle at your favorite electronics store to get a feel for how to set up your input devices.

Though it could theoretically feed its output to a line-level amplifier, the converted stereo has enough power to make an amplifier unnecessary. With the stereo in the dashboard, hook up your speakers (most anything with 4 ohms of impedance that can handle at least 45 watts will work; usually, the more you spend on speakers, the better your stereo will sound), connect it to a 12-volt power source, and rock out with your bad self.

Just don’t hold me responsible for any disturbing-the-peace tickets you might receive.


Written by Daniel Strohl and Posted with Permission of CarTechBooks


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