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.
This Tech Tip is From the Full Book, HOW TO BUILD MAX-PERFORMANCE PONTIAC V-8S. For a comprehensive guide on this entire subject you can visit this link:
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://www.pontiacdiy.com/mastering-gto-restorations-electrical-guide/
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.