1977 Ford F-150 Wire Harness Install - Wire Transfer
Rewire Your Entire Truck
One of the most appealing qualities of old trucks is that they are simple, which generally makes them reliable—and easy to fix when they are less than reliable. That was the situation we were in with our Cheap Truck Challenge Ford F-150, Raymond (“Raymond,” Oct. ’13). Nate’s Precision had upgraded the truck with a 460 engine from LA Speed, an Offroad Design Doubler, and Super Duty axles, but electrical gremlins had left us on the side of the road more than once. This is a simple truck, with a manual transmission, a carbureted engine, and no computers to speak of. As we looked for the cause of the issue we thought we found the smoking gun more than once, with loose wires, poor grounding, and household wire nuts added at some point in the truck’s life. Instead of giving us confidence that the issue was resolved, the more closely we looked at the wiring the more problems we found.
Instead of patching and splicing pieces together, we decided to install a completely new wiring harness from Summit Racing Equipment. This would eliminate all of the wire nuts and Scotchlok connectors and upgrade our old glass fuses to modern mini blade fuses. Since this is a “universal” harness the wires are longer than necessary, it has wiring for items like air conditioning that our truck doesn’t need, and it does not come with any plugs for the taillights or factory gauges. We underestimated just how big of a project this would be, and our truck was down for nearly a month while we devoted a couple of nights a week to rewiring the Ford. If you and electricity don’t get along this might be a job best left to the pros.
Since we were revamping the electrical system, we added a high-output, one-wire alternator from Summit at the same time. The 140-amp alternator feeds dual Odyssey Group 78 batteries that we mounted under the hood in Trail-Gear battery boxes. The spacious engine bay and flat inner fenders made the install simple, and now we never have to worry about running out of juice, even when heavy winching. The end result doesn’t have the same visual impact as a new set of mud-terrains or a winch bumper, but it will keep our old truck reliable for years to come.
The Summit Racing Equipment 18-circuit wiring harness was plenty long for our regular cab, shortbed truck. It also had more circuits than we needed since we are not running items like an electric fan or trunk light. You can cut the extra wires out, but we tied them out of the way in case we want to add electrical accessories in the future.
Each wire is labeled to simplify connections and save time. Summit also includes a full key of the colors and designations is the instructions. This was very helpful when laying out everything under the dash or under the hood.
The new fuse block replaced our old glass fuses with mini blade fuses that are more robust when subjected to vibration off-road. They are also easier to source than glass fuses. Our only complaint was that the Summit fuse block did not come with a mounting bracket.
The cover for the fuse box has all of the circuits labeled, just like a factory box. This makes troubleshooting issues much easier, but if you appropriate something like the power windows to run your LED light bar, make certain that you update the labels to match.
This is what we were up against. Butt connectors, Scotchloks, and twisted-together wires may have started as field fixes but were still found on our ’77 F-150 years later. They contributed to blown fuses, short circuits, and lights that only worked sporadically.
No going back now! Originally we planned to trace each new wire next to the old wire, but that proved impossible since we did not want to drill another hole in the firewall to run all of the new wires. Instead we cut all of the old wires and started fresh.
This is the pile of wiring and components that were removed. We were really able to clean up under the hood since our MSD ignition had replaced the factory Ford ignition box and our new Summit alternator is internally regulated.
We used Weatherpak connectors to splice in at the end of the new harness. When possible, we replaced the factory plugs for circuits such as the brake lights and turn signals, but when new parts were not available we spliced in to the existing connectors. Since this is a universal harness it does not come with any connectors.
The underhood wiring was fairly straightforward. We matched up the new wires to the old wires and then removed the old wiring. After we had everything tested and running we added wire loom to the whole thing for a better appearance under the hood.
In addition to the wiring harness we sourced high-quality electrical connectors and heat shrink from Summit. This took a little more time but resulted in a clean, durable finished product.
Our new Summit alternator fits in the stock mounting brackets but provides nearly twice the amperage of the factory alternator. It also only needs one wire to run and is internally regulated, making it an all-around win.
Odyssey Group 78 batteries feature 850 cold cranking amps and 135 minutes of reserve capacity. We added one to each inner fender with a Trail-Gear battery box to hold them firmly in place and made our own battery cables from welding cable. We should never have any issues starting our high-compression big block or running our Warn winch.
While the rear of the truck and under the hood were fairly straightforward, the interior wiring was not. It would have been much easier if we had abandoned the factory gauge cluster for some Auto Meter gauges and toggle switches.
Alex Baker has about 20 hours into wiring the interior of the truck. “I could have done it more quickly,” he quips, “but I assumed that you wanted everything to work when I was done.” This is not a job for the impatient.
The factory gauge cluster has a connector on the back with a dozen wires coming out of it. We picked up a Chiltons manual with wiring diagrams in it and then traced out the wires individually before splicing them in to the harness.
Once the column and gauge cluster were wired we added loom and zip ties to secure everything in place. The end result looks and performs great, but it was not quick or easy.