The wiring systems of the 1964– 1974 Pontiac GTOs are probably closer in complexity to a Model T Ford than anything currently in showrooms. While that may be true, wiring systems are still a point of fear and loathing among many restorers of Pontiac GTOs and other muscle car era machines. The truth is, it really isn’t that bad if you plan ahead. Armed with a decent set of tools, a little patience, and a shop manual with complete wiring diagrams, you are able to restore function to those areas of the electrical system that are no longer operational.
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Over the course of 40 or more years, it is likely that your GTO, like any vehicle that age, has developed some wiring problems. Perhaps the backup lamps no longer work or a power window is no longer operational, and maybe the engine won’t fire. In that amount of time, wiring may deteriorate, grounds may fail, or perhaps some past owner tried to install aftermarket gauges and needlessly started hacking away at wires, causing shorts and other problems. Whatever the case, the goal is to get everything working reliably and as originally intended.
The wiring condition is probably a pretty good indicator of the condition of the rest of the car. If your car was well taken care of, chances are you will have less trouble than a GTO that had been abused the majority of its life. Since I have not advocated the restoration of GTOs that are clearly good for nothing other than parts, I assume that the electrical system is generally in decent shape but in need of some help.
Vintage radios can be restored at home if you have the skills or by a number of companies such as Antique Radio Doctor. If the radio still works, you can restore the push-buttons, face, and knobs, so it appears factory new. Remove the face plate, clean out the dust, and put a fresh dab of red paint on the sta¬tion indicator. Replacement knobs and face-plate decals are available from most restoration parts suppliers and fishing line can be used to repair the loss of movement on the station indicator. (Photo Courtesy Scott Tiemann)
Of all the electrical connections on your GTO, chances are that the battery cables and terminals have seen more use and abuse than any other part that carries current. Often, the terminals have been overtight¬ened and distorted. Also, jumper cables have gouged them and battery acid has cor¬roded them. If the cables on your battery are still in decent shape, they can be cleaned up along with the battery terminals. If they need to be replaced, make sure that you get cables of sufficient gauge thickness; it is more important than how they look, as cables that are too thin can cause too much resistance and can heat up. Unless you are competing in concours judging, pass on 6-gauge battery cables and reproduction tar-top batteries. Get a modern replacement battery and at least 4-gauge cables. These batteries cost less and work better than the originals ever did. (Photo Courtesy Imran Chaudary)
In this chapter I show you how to repair the consequences of an electrical fire or other catastrophic failure, several trouble spots, and what you need to do for a successful outcome. I also show you some upgrading options that can be easily added for more convenience and enjoyment.
While it certainly is not the cause of all electrical problems, more often than not, a faulty ground is the main source of trouble, especially in a car of this age. Over the years, ground wires and straps become corroded, break, or fall off, and fray to the point that they no long conduct electricity. Ground straps are particularly important on a full-frame car, as they provide a path between the body and frame where electricity can flow. With the body isolated from the frame with rubber body mounts, interior electrics really have no way to complete a circuit without them. Unibody cars do not have this level of reliance on ground straps like a conventional body-on-frame design, but even the stub-framed 1974 GTOs need them more than a modern car.
A wiring diagram from your shop manual lists the number of grounding points and their locations. If they are missing or no longer functional, correct replacements are available.
Once the grounds have been attended to, it is time to move on to the other connections in the car. A multi-tester is a very handy and useful item for tracking down shorts and bad connections.
Inspection of the Wiring
Before you begin the inspection, take stock of your car’s electrical system. Make notes about which electrical parts work and which are non-functional. Are all of the lights working, including the license plate lamp, the reverse lamps, and the interior lighting? What about the cigar lighter? Is the element burned out or is the socket not working? (Yes, they are cigar lighters, not cigarette lighters; check your owner’s manual.)
Once you have a complete list of electrical components that are not working, take the time to familiarize yourself with the wiring diagrams in the shop manual before taking any direct action. This gives you the opportunity to isolate each trouble spot and figure out where the most logical failure point is. Problems can usually be traced to a switch failure, break in the wiring connection, faulty ground, or defective device, be it a bulb, motor, or radio. Use your multi-tester to see if power is actually getting to the device. If it is, the device is malfunctioning. If not, look for the connection failure.
Internal breaks in the wiring are often found with a multi-tester, and they can be tough to get at, often showing up in plug-in connectors in plastic or rubber housings; they are in turn part of a larger harness. Sometimes, it is a simple fix, as when a wire was pulled and stretched enough that it came out of the back side of a plug-in connector. Perhaps a plastic wire insulator cracked with age and exposed a bare wire to some bare metal and a short was caused. Keep an eye out for obvious problems like that.
After 40 years or more, ground straps are often frayed, corroded, or even broken. Those in good condition and with a solid chassis connection are especially important on full-frame cars, such as 1964-1973 GTOs. These provide a path for the electricity to flow between the body and the frame and therefore allow the circuit to be com¬pleted. Rubber body mounts isolate these units, and for the stereo and lighting system to properly function, you need the ground straps in good working order. The number of ground straps varies from year to year and generation to generation, so check with your shop manual for their location on your particular car. Replacing them is a snap; just unbolt them from the firewall and the frame and bolt in their replacements. Use new washers, remove corrosion, and clean the area to the bare metal for the best contact. (Photo Courtesy Scott Tiemann)
The wiring passes from the front of the car to the rear. Most notably, the wiring for the taillights and reverse lamps, as well as side-marker lamps, are routed and protected by plastic or rubber tubes. These tubes keep the wir¬ing dry and safe from the constant rubbing caused by passenger footwear on the carpeting. Most often these tubes are in good shape and can be reused, as long as the carpeting is intact on your car and the floorboards aren’t rusted out. Use a multi-tester to make sure that all the wiring is still func¬tional and replace the wiring that does not complete a circuit. Simply connect the multi-tester’s probes to the connections to see if current passes though the wiring. If it does, the gauge on the face of the multi-tester moves to show the current flow. If if doesn’t, it stays at zero. (Photo Courtesy Scott Tiemann)
A wiring diagram causes nightmares for many car enthusiasts, and that includes me. The thing to keep in mind is that while the wiring diagrams in your shop manual are not going to look exactly like this, they nonetheless illus-trate where everything is and what everything does. Testing individual pieces, figuring out if there is a wiring issue, a ground issue, or a blown bulb goes a lot faster with a multi-tester, such as one from Radio Shack. (Photo Courtesy Scott Tiemann)
A wiring harness is a wearable item, and after more than 40 years, it may be simply worn out. If you’re performing a complete restoration, it’s a good opportunity to install a new harness. Routing and securing the harness is much easier if the engine and interior have been removed because you have full access to do the work. If your wir¬ing harness has been substantially damaged, burned, or deteriorated beyond repair, you need to install a new one.
Painless offers exceptional reproduction wiring harnesses. Its universal GM muscle car kit fits all GM A-, F-, and X-Body cars from 1964 to 1974 and an optional engine compartment harness can also be included. It is a more generic version of what was offered in the cars originally and uses standard GM plugs, fittings, and color coding. Installation can be accomplished using the same procedures as for a factory-original harness. This kit even includes labels for connections, which makes the installation, well, painless. The system includes comprehensive instructions, which can be downloaded from the web¬site. (Photo Courtesy Painless Performance Products)
The starter relay is exposed to the elements, and as a result, it tends to fail. Fortunately, it is a fairly simple item to get at and to repair or replace. Use a multi-tester to measure the voltage and resistance and then compare them to the actual specs. Also, inspect the wiring to the relay and determine if there’s any damage such as cut, chafed, or frayed wires. When the relay fails, often it’s just a matter of cleaning off all the terminals, and the starter is opera¬tional again. However, starter relay replacements are inexpensive and plentiful through most restoration parts houses. (Photo Courtesy Scott Tiemann)
Before you start cutting into wire insulation or taking plug-in connectors apart, make sure that replacement pieces are available. The good news is that many of these pieces are still available or are being reproduced. Lectric Limited has become a great source not only of harnesses, but also of correct switches, ground straps, connectors, bulbs, and other items that help get your electrical system back to its original operational condition.
The repairs themselves do not end up looking exactly like the original wiring, but that is not a problem, most of it is not visible anyway. It is important that the repairs are performed correctly and are as durable as the circuit was when new, if not more durable. That means splicing the wires together and then soldering them with resin-core solder and covering the bare wire connection using shrink wrap. From there, it needs to be heated with a hair dryer or heat gun for a permanent, weatherproof connection. This is no place for a quick wrap of electrical tape or other solutions that won’t last. You don’t want to be pulling up carpeting or taking apart your dash again. Do it right and do it once.
Harness Replacement
If the wiring harness is just too brittle, broken down, and deteriorated to provide any more useful service, you need a replacement. Again, the aftermarket has OE-quality replacements that bring function and reliability to your electrical system. Replacement harnesses are available from Painless Products and Lectric Limited; they are very nice, very robust units. There are some differences, though, not based on quality but by application.
Lectric Limited has two series of harnesses the Original Design Series and the Custom Update Series. The first is an exact-reproduction wiring harness, manufactured using the original GM blueprints, with the correct color coding, connectors, and wrappings. You can order exact-replacement dash, engine, and front and rear lamp harnesses. This is a great choice for concours and stock driver restorations, as it is a harness designed with production-style components and has a very authentic appearance.
The Original Design Series also allows for some minor modifications. Lectric Limited has already designed modified versions that accommodate some commonly-requested alterations from stock, such as adding HEI or a newer alternator, as well as alternator relocation. These changes can be added to the basic wiring layout.
Depending on the year and the option level, a GTO could be equipped with a 37-amp alternator. That was barely enough to charge the battery and keep the car running at the same time. Low-amp alternators were great for race cars because they didn’t use as much power to turn them. But if you are adding any power options, it makes sense to upgrade to a higher-amperage version.
Installing an alternator is one of the easiest things to do on a GTO. First, remove the battery cables from the terminals, mak¬ing sure they don’t come in contact with the terminals. Loosen the bolts that hold the alternator to the mounting bracket. This creates slack in the belt so it can be removed. Disconnect the terminal and the ground wire attached to the back of the alternator. Remove the bolts securing the alternator. Place the new alternator in the designated position and torque the new bolts. Plug the terminal back in and attach the ground wire at the back of the alternator. Slip the belt over the pulley and push the alternator up with your hand. Use a flat-head screwdriver to push against the belt. You should be able to push it out 1/4 inch to obtain the correct tension. Torque the bolts to hold the alternator in this desired position. Reconnect battery terminals.
Compatible units with up to 200 amps are available from Year One and others if you are adding EFI and an in-car entertainment system. Lower-amperage versions are also available for restorations with more modest power requirements.
Although the alternator is usually blamed for charging problems, you need to check on the voltage regulator as well. Look for breaks in the circuit and use a multi-tester to confirm the resistance ratings in the shop manual. If clean¬ing the contacts still does not bring the readings to spec, replace it. If it is not operating properly, the alternator cannot properly charge the battery, prevent¬ing long-term operation. Replacements are readily available and installation is a plug-and-play procedure.
A high-performance modern electronic dis¬tributor can be a visu¬ally subtle change, but it also pays big divi¬dends in performance and convenience. This unit, manufactured by Pertronix, replaces the breaker points, so the spark consistency is stronger and more precise. As you know, points are wearable items, and over time the gap needs to be maintained for maximum performance. Even under perfect adjustment, an electronic ignition provides a more powerful and precise spark than a points ignition. The spark is also much more intense, which increases power and mileage. While converting the standard points-type distributor to a later GM HEI unit has been a popular upgrade in the past, it is visually incorrect for a 1960s-era car. If your GTO is equipped with a Tri-Power system, an HEI interferes with the rear carburetor and as a result, does not fit. This conversion does a great job of bringing your ignition system performance up to date without sacrificing your authentic-look¬ing engine compartment. It is a simple modification well worth the cost. (Photo Courtesy of Pertronix Corporation)
If you are upgrading your ignition system with an electronic distributor module, a coil upgrade is also necessary. This Pertro¬nix coil is designed for compatibil¬ity with its module and provides lower resistance. Make sure your ignition components are all compat¬ible, as damage or lack of ignition can result. (Photo Courtesy Pertronix Corporation)
The Custom Update Series is a great solution to updating the wiring for modified vehicles, so if you’re looking to do a full pro-touring style of build, you have that option. This harness is a little more of a do-it-yourself approach to wiring and you need to cut the wiring to the desired length and add the connectors yourself. The upside is that you can design a custom system for your exact needs and save some money by finishing it yourself.
The Painless wiring kit is a universal GM kit designed for 1964– 1974 intermediates, as well as F- and X-Body cars. Knowing that most of the GM mid-size offerings were more the same than they were different, especially from an electrical standpoint, Painless engineered a wiring harness that works with any of these vehicles. Although the kit uses standard GM plugs and other hardware common to these vehicles, it is more of a Swiss Army knife approach it is not a perfect reproduction product but it is designed to be a functionally identical replacement for GM’s offerings from that period. Like the Lectric Limited approach, you can mix and match different harnesses, such as interior, engine compartment, and front and rear lighting; and there are options within those items as well. Once the harness is installed, its deviations from the original design would take some serious sleuthing to detect.
Trouble Spots
Every Pontiac GTO model year has idiosyncrasies and problems; the service bulletins help solve those problems. However, there are common areas that affect all Pontiacs and likely all GM cars from that era. Most are associated with age.
Starting System
Starters and starter solenoids can wear out over time; ballast resistors can also be the culprit. Since there are still a lot of Pontiacs from this era on the road, finding replacement starters, solenoids, and accessories is pretty easy. Even high-torque versions are available if you have a hard-starting, big-inch engine with a lot of compression. Of course, if this is a concours-style restoration, you have to rebuild your original pieces, which is much more expensive. It is likely that a rebuilder in your area can handle the job.
Ignition switches can also be problematic, and dash-mounted switches can become especially loose. It is not unusual to find mid 1960s era Pontiacs that can be started with a screwdriver. If they can get that sloppy, they can also fail to complete the circuit and leave you without a means to get your car started and running.
Charging System
With an older car, the charging system, like other areas of the electrical system, is prone to grounding issues, which can put additional strain on the alternator and voltage regulator. When repairing or replacing these components, be sure to replace all of the ground straps to ensure the proper function and longevity of these refurbished components.
The alternator wears out over time, and if your original, correctly date-coded unit is in need of rebuilding, it is something that can be done at home, or it can be commercially performed. Most kits include detailed directions and the job can be handled with normal hand tools.
Upgrades
Upgrading the charging system in the quest to make your driver-quality GTO a better-performing machine is important. An upgraded stereo, high-performance ignition system, electric fans, and add-on air-conditioning system all contribute to the electrical demands made on your charging system. A stock alternator is hard-pressed to keep up.
Although concours judges like to see a set of original T-3 headlamps with the molded-in triangle, the truth is, they were not that great, performance-wise. A modern set of replacement sealed-beam headlamps is a wise addition to a driver-type restoration. As an example, Hella H-4 lamps are a huge improvement over the originals and are available just about any¬where, including Amazon.com. Just be sure to save the original T-3s, if they are still with the car, as they are quite valuable. (Photo Courtesy Scott Tiemann)
If your car has an aftermarket tach or other accessory gauges installed, the decision to retain them is based on your restoration type and their condition. If you are performing a concours-style resto and none of the gauges work, remove them. If they are period-correct and you are performing a weekend driver restoration effort, it is worthwhile to retain them. In the case of this car, a 1964 Royal Bobcat GTO, they were retained, as the car was restored not to 100-percent stock, but to the configuration that it was in when it was featured in the March 1964 issue of Car and Driver magazine. Since the gauges were in very good original condition, they were simply disassmbled, cleaned, and re-assembled. (Photo Courtesy Scott Tiemann)
In the mid 1970s, GM replaced the old-style alternator having the external voltage regulator with a more modern, SI (systems integrated) series, single-wire alternator with the internal voltage regulator. It offered more charging power and reliability, as the regulator was more protected from the elements. Converting your GTO to take advantage of these newer alternators is a simple procedure. Conversion kits are available from several sources to upgrade your system to maintain those elevated requirements.
Higher-amperage SI alternators are a sensible upgrade that helps your car handle the additional strain. Units up to 200 amps are available from Year One and other sources that can be adapted to your GTO. A power level like that more than covers any upgrade in your plan.
Ignition
The ignition system actually gives you a lot of warning that things are amiss. With hundreds of millions of revolutions over the course of its life, the ignition has no doubt deteriorated somewhat over time and is likely in need of some attention.
Other than when it gets wet, the ignition system rarely leaves you hanging. As it wears, however, the performance of your engine gradually reduces until it starts misfiring, running rough, and dropping a cylinder or two. The main causes for this sort of trouble are the distributor cap, breaker points, plug wires, and plugs themselves.
Replacing the distributor cap, wires, and plugs is simple. As the wires get older, their resistance increases, and less electricity makes its way to the plugs, reducing performance. Recent advancements in plug wire technology bring new levels of performance with a new generation of low-resistance wires that still look like factory items.
Like the radios, original speakers can be reconditioned and restored to like-new appearance and operation. Most radio restoration companies also service speakers. Reproduction speakers are also available. If appearance is not a concern, much higher quality speakers can be substituted and fit into the stock locations. (Photo Courtesy Scott Tiemann)
The stereo in Les Iden’s 1966 GTO is an interesting blend of old and new. The car features a reproduction of the 1966 Pontiac A-Body AM/FM radio from Antique Auto Radio. It looks authentic on the outside but uses all modern internals. With a shallower chassis, it allows for easier installation and features mini-plug inputs so you can hardwire an iPod or satellite radio receiver directly into it. It also features 45 watts of power in each of its four channels and is an excellent alternative for those wishing for modern sound with an authentic look.
Spark plugs wear over time as well and should be replaced, taking the time to read the old ones for signs of engine condition and possible problems. Engine builders have preferences for various brands and it never hurts to hear what their recommendations are for your particular engine combination.
Replace the breaker points on any street-driven restoration with an electronic control module and compatible coil, like those from Pertronix. They add to the efficiency and intensity of the spark, making the most of your new, low-resistance plug wires and fresh spark plugs. More spark translates to a little more power, a little better fuel economy, and reduced exhaust emissions. It’s a very worthwhile addition to your street-driven GTO.
Lighting
Even though the wiring system for your GTO’s lighting is fairly simple, it can still cause problems and more often than not, those problems are related to the condition of the sockets for the bulbs and the grounds. Check the shop manual to determine where the lighting grounds are and how many there should be; and make the necessary repairs to bring them back to factory specs.
Next, inspect the lamp sockets for corrosion and damage. Clean the terminals of all corrosion and make sure they are making proper contact with the bulbs at their particular connection points. Headlamps have prongs that fit into their sockets, while most of the rest of the bulbs use barrel-type sockets. Order and install new sockets and bulbs as needed.
The original T-3 headlamps were good for their day, but newer replacements are readily available that provide superior illumination for night driving. This is another safety-oriented upgrade that can be easily integrated into your driver restoration. If your car still has any operational T-3 headlamps, remove and safely store them, as even used ones command a hefty price from concours restorers.
Audio
Providing a great-sounding but authentic-looking sound system has been a problem for muscle car fans either you had one that looked authentic or you had one that sounded great. For some reason, the two really didn’t mix, even though promises to that effect were commonplace right up to a few years ago. Unfortunately, most of them were underpowered and overpriced junk. I hate to see a late-model aftermarket stereo in the dash of a classic muscle car because it just looks so incorrect. I am not a purist by any stretch, but the clash of design eras just comes off as clunky, unintegrated, and anachronistic. I like old and new, just not in some grotesque Frankendash mismatch.
I recently photographed a car feature on my friend Les Iden’s modified 1966 GTO for POCI’s Smoke Signals magazine and must admit, I was completely fooled by the head unit he had in his dash. I thought it was a stock 1966 A-Body radio. When he told me he had a custom sound system, I asked if he hid it in the glovebox. He said that it was right in the stock location. I had to do a double-take.
Upon closer inspection, I was amazed to find an extremely stealthy and really fantastic-sounding AM/FM stereo. Manufactured by Antique Auto Radio, this head unit fits in the stock location but is only about 3 inches deep, taking up less space than a stock radio. This unit also accepts auxiliary inputs from an iPod, mp3 player, or a satellite receiver. It’s a great-looking and great-sounding system. If you like to bring your music with you, this is a very viable option. In the case of Les’ 1966, the shallow chassis dimensions were especially helpful since he had added an aftermarket air-conditioning system and needed the room behind the radio for ducting.
In addition to the 1966 A-Body Pontiac, Antique Auto Radio also offers a similar reciever for 1969–1972 A-Bodies, and more will undoubtedly be released in the future. Custom builds are also available that can fit in stock radio chassis for vehicles not listed.
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