When restoring vehicles, wiring can make or break your project. Chances are even if you original wiring did work its crusty, brittle and on borrowed time. The last thing you want to do is put an old harness back on your project and end up chasing electrical gremlins that prevent you from enjoying your vehicle. What are your options? You can patch together the old wiring which is not ideal. You could try to find an NOS harness that may be just as brittle as the one you have and set you back a bunch of money. Lastly you can make a completely new harness using your old one as a pattern.
While restoring my 1981 D150 I came to a crossroad about the wiring. The existing wiring was in working order but was crusty and many of the connectors were damaged. I did not want to put that back on my freshly painted frame and engine bay. I initially thought that since it was working, I could just replace the broken ends and rewrap the harness. After pricing out the replacement connectors and thinking of all the splices id have to make, I decided that it would be simpler to make a new harness. This route would also make it easier to integrate the new circuits needed to run the efi system and update the harness with modern materials.
The first step I took was to unwrap the old harness to see what color and gauge wires I needed. This is also helpful to understand how each circuit is run and where grounds go. While unwrapping the harness I used zip ties to keep the harness branches in the correct locations. Once the harness is unwrapped, I made a list of the needed connectors and wire colors needed. In this application I elected to update as many of the connectors with modern weatherproof ones where I could. I used Deutsch DT series connectors from Summit Racing. They offer assortments with and without the crimp tool that can be found here. I sourced wire from AC/DC Wire and Supply on eBay. My harness is 16GA and I was able to order 25ft lengths of each color needed. All the other connectors and bulb sockets that are specific to the vehicle I ordered through Rock Auto.
While I was waiting for the components to arrive, I started to look into what to cover the harness with. Protecting the new wires from chemicals, heat, and abrasion is important for long term durability. Modern vehicles are a great place to look for inspiration on what to use to protect the harness. Gone are the days of basic electrical tape to wrap wiring. Basic electrical tape has many drawbacks. It melts, gets brittle, and is messy if you need to make a repair. I chose to use Tesa 51036 fabric tape for its high heat and chemical resistance. To protect for abrasion, I used Alex Tech PET braided expandable sleeve.
Once all my materials arrived, it was time to start laying out the new harness. It is a great idea to draw a diagram that labels each plug and laying out what colors go to it. I found it helpful to ensure I had the right number of wires going to each plug. With the diagram complete I laid the old harness out on the floor to start pulling the new wires to the correct lengths. In my case some wires had splices in them where it would split into multiple wires. This is often the case for grounds and common power wires. To make these splices I soldered the wires together for a strong joint that was then covered with heat shrink tube. With all the wires all laid out with the correct lengths and the branches separated out it was time to start wrapping the harness. I wrapped nearly every inch of the harness with the Tesa tape and then slid the appropriate size expandable sleeve over the taped sections. I used heat shrink tube or tape to seal the ends of the sleeve.
With the harness completely wrapped it was time to start pinning out the connectors and installing them. The Deutsch DT series connectors use crimp on pins that are inserted into the connector body. Once the pins are inserted then the lock piece is installed followed by the weatherproof seal. I found these connectors very easy to work with and very high quality. The crimp tool that comes with the Summit Racing kit was adequate but I'm sure better tools exist. Once the connectors are installed you have a completed harness that looks factory to install on your project.