Looking back on our recent feature trucks, it's no surprise that the '60-66 Chevy and GMC trucks have become popular for both restoration and rodding. The choices for updated suspension, braking, air conditioning, and replacement sheetmetal have added new life to these trucks.
One of the most critical but overlooked areas in any vehicle update is the planning and design of the entire electrical system. The power requirements of the most popular accessories incorporated into most buildups today can far exceed the capacity and capability of the original electrical system. While original replacement harnesses and their associated circuits are correct for a period restoration, they can be seriously compromised when overloaded with upgrades, such as electric windows and locks, electric fuel pumps, EFI, electric seats, electric fans, etc. When you realize that the word electric appears in every one of these common additions, it's easy to realize that an electrical-system reevaluation and update is in order.
Let's look a little deeper into the wiring on the '60-66 GM trucks. The original electrical system used PVC wire and is under-gauged by today's standards for all power circuits. The system was designed around four major harness groups: dash, engine, front lighting, and rear body. That design concept is quite good, however, for a '60s vehicle that had few electric options available, it tends to seriously limit update options. As an example, the heart of the system (the dash harness) was not required to provide a large number of fused power circuits for system protection, and the fuse box reflects this point. Additionally, the front lighting handled a standard sealed beam headlight, and the stock alternator was an external regulator design with an output of 32 amps. Hopefully, you can see the dilemma we will be faced with when we attempt to add accessories to this system.
The basic capability of the entire system is not the only issue. Any new system has to be able to interface with the system design configuration of the original vehicle. Things like parking-light sockets, taillight sockets, all dash switch connectors, steering-column connections, the front grille lighting interface, HVAC control head and resistor controls, etc. are specific to the vehicle and must be considered in any redesign of the electrical system. The point is that a generic solution that doesn't take these things into consideration is no better than the system it replaces.
It's no surprise that millions of factory dollars have resulted in better terminals, better heat- and abrasion-resistant wire, and more secure connectors. While these are all available for use, it still comes down to making any new system work within the original design constraints of the truck. Often overlooked in projects are heating and A/C systems, wiper systems, original light sockets and connectors, dash and instrument-cluster configurations, and switch mounting. When planning your project, it's important to consider just how much of the original truck will remain as part of your new design. For instance, the original instrument cluster in all '60-66 trucks used a trim plate into which a gauge panel was mounted. While we can replace the gauge panel with many different gauge packages, the original trim plate is usually retained. Take a look at your truck and you will see that the original trim plate provided the mounting for the headlight, ignition, and wiper switches and, more than likely, will require a significant amount of rework to change. The same would hold true for the heater control panel.
We contacted American Autowire/Factory-Fit when we heard they had developed a new kit in their Classic Update Series line specifically for the '60-66 Chevy and GMC trucks. We have used factory replacement Factory-Fit harnesses from American Autowire on previous projects and know their experience with the entire vehicle electrical-system configuration. Previous projects in this magazine have detailed their Classic Update Series kits for the Chevrolet and GMC '47-54 and '55-59 trucks and found them to be extremely well-engineered and easy to install. However, we were particularly interested in how their new kit tackled the many differences in factory options offered for the '60-66 trucks.
There is quite a bit of valuable information in the instructions included with this kit, and we were pleased to see the same attention to detail and engineering as their previous kits. As our test vehicle, we used a stock '65 C-20 Fleetside that was in serious need of a rewire. This kit is designed to provide the most complete under-dash wiring as possible with minimal termination work for the installer. This is great as few of us like to spend a lot of time crawling up under the dash. The remainder of the truck is more generic to allow any custom routing scheme desired by the installer. This combination with the detailed vehicle-specific instructions made our installation easy and our truck electrically secure.