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.
The ignition switch wiring can accommodate either a dash-mounted ignition switch (supplied in the kit) or a later-model column-mounted ignition switch (the terminals are the same). To use the column switch you have to remove the dash-mounted ignition-switch connector and replace it with the two-column mounted ignition-switch connectors supplied in the kit. | 
The heaters used in these trucks also varied in switch and blower-motor connections. The connection to the dash-mounted ignition switch and the heater are shown here. Many aftermarket A/C and heater units, such as the Vintage Air units, are made to work with the original heater control head. Having the correct connection to the original switch is important. Thankfully, everything was there to make any of them work. | 
Here's how a new wiring system should look, nice and neat. There are many gauge insert panels in the aftermarket, but most are inserts that must use the original dash surround plate. The gauge disconnect feature (see arrow) easily accommodates different gauge styles. |
The original dash cluster in our '65 truck was a warning light cluster, but optional factory gauge clusters were available that replaced warning lights with actual gauges. Note that original gauge clusters used an ammeter. The AAW kit handles the charging system with a voltmeter. | 
We wanted to try a few different gauge configurations to test out the ease of wiring different gauges to the dash disconnect. The RB's Obsolete brushed aluminum gauge panel looks great with the Auto Meter gauges. High-beam and turn-signal indicator lights are 5/32-inch LEDs. | 
The wiring of each gauge was clean and straightforward. With the disconnect feature, we wired the instrument cluster on the bench. Electronic programmable speedometers are becoming the standard in aftermarket gauges, and we found it a real plus that the connector was supplied in the kit. |
RB's Obsolete offers another insert filled with Classic Instruments' gauges. The wiring of each gauge was different than the Auto Meter setup, but the kit easily handled those differences. This speedometer does not use the eight-position connector that the Auto Meter speedometer uses. The calibration is accomplished with an 8 DIP switch on the back of the case. | 
The last panel we looked at was the Dakota Digital cluster that uses an interface to a control box. The wiring in this case went to the control box instead of the back of the instrument cluster. Connection to the control box is made under the dash before the complete Dakota Digital instrument cluster was installed. | 
We chose to use the Classic Instruments cluster. Wiring was a simple matter of plugging the two mating connectors from the dash harness to the gauge harness. Note the two twisted wires in the cluster disconnect. These are the signal and ground wires from the vehicle speed sensor (VSS) used by the electronic speedometer. As per the manufacturers instructions, these wires were twisted to cancel out any signal interference. AAW recommends this practice for all electronic speedometers and provides plenty of wire to do it. The completed cluster was then set in place. |
Unlike the under-dash harness, the engine and front-lighting harnesses need to be flexible to accommodate any custom wire routing. The kit provided plenty of wire for this task. The connections for the distributor, coil, temperature, alternator, and oil pressure can be routed in any desirable configuration. We chose to use the stock hole located close to the back of the engine and ran our connections along the back of the engine and down the side of the intake manifold in a protected covering. | 
The running lights and turn signals are mounted in the hood so we had to run the wiring under the hood structural support. All the harness retaining clips and correct light sockets are included. | 
The connection between the under-dash harness and the front-light harness can be made through the original hole with the original factory-style bulkhead grommet. There's enough wire length, though, for any custom wire routing if you have smoothed your firewall. |
The headlights are plugged in through a special connector located on the radiator support (see arrow). While the kit would have let us route the wire differently, we chose to use this connection because the entire headlight grille assembly must be bolted to the front sheetmetal as a unit. This will require a wire disconnect for the headlight grille assembly. The kit supplies the original mating disconnects for this purpose. We also chose this location to mount an electric fan relay. | 
Shown here are the headlight connection and the waterproof connector that plugs into the radiator support before the final bolt-up of the headlight grille assembly. Our '65 truck requires a single headlight connection. The kit also provides dual headlight connectors that are used in the '60-61 Chevys and all GMC trucks. | 
The rear body wiring was connected to the under-dash harness and routed to the rear of the truck along the floor under the threshold plate. This made it easy to attach the overhead courtesy light and the fuel tank sender. We kept the fuel tank in the stock location, but in applications where the tank is moved under the pickup bed, the sender wire would be routed with the rear lighting to the rear of the truck (plenty of wire is supplied). |
Original terminals are provided to work with the overhead courtesy light mounted at the roof panel. We routed the wires through the cab inner panel. | 
Fleetside and stepside rear light assemblies used a special light socket for the stock taillight housings. The kit includes these light sockets, as well as the waterproof boot and tube assemblies used to protect the wiring within the pickup bed. Here you can see the new components next to the original pieces removed from our project truck. | 
Backup light assemblies were optional items in these trucks. Reproduction replacement assemblies are available, and the kit contains the correct terminals and connectors to add these units. |