Where to begin?? Fair warning, this is going to be lengthy. I’ll have to cut this down and simplify for some of the forums but here I’ll post all the details.
For the engine swap, the minimum wiring to get the thing fired up isn’t bad, particularly if you opt to have V8R prep the engine harness for you (I did). You could certainly retain most of the factory wiring on the chassis side and just tie in where needed.
However… I had a few things on the wish list for this car that meant there was more work to do.
Over the years of racing and modifying this car, the wiring has become a bit of a mess with things added, wiring cut to remove things, etc. etc. There’s even been a couple times in the past that I went to modify or fix something in the wiring and found it wasn’t the way the FSM says it should be – I had modified it at some distant time in the past and now I couldn’t remember how or why I did it.
To eliminate any potential for issues for the future, I decided the best approach was to remove all of the existing wiring on the chassis side from the car and start from scratch with good materials, practices, and documentation. This is also the most time consuming approach, but c’est la vie.
Step 1 through 10 of a big wiring project is all planning, long before any tools or wires come out. Drawing up plans, thinking about the systems you want to include and things you may want to incorporate in the future.
Here was my starting point, the electrical diagram for my new chassis wiring:
A diagram like this is the bare minimum to plan out a harness. But as soon as you go down this path, if there’s an issue in the future you can’t just open up a factory service manual to check the wiring diagram. None of that applies any more. The ease or difficulty of service/troubleshooting in the future now comes down entirely to the quality of the documentation you create. With that in mind, I took things a few steps further.
Working off the electrical diagram, I made a spreadsheet listing each individual wire that would be present in the harness – including the wire’s name/purpose and where each end terminates. Each wire is assigned a unique numerical ID. If you’ve ever tried to identify a certain wire in a harness you’ll know the struggle that can be – even with the multitude of wire colors that factories use you still end up with duplicates of certain colors and you end up having to break out the multimeter to test wires and sort out what’s what. By assigning each wire a unique ID and labeling the wire accordingly (more on that later) there is no guesswork left to do, just consult the master sheet and look up the wire number.
Here’s a screenshot of the top of the list. All in, there’s about 100 wires on the chassis side:
A great feature with having this in spreadsheet form means that if you stay consistent with the info you put in each cell then once the list is done you can sort the list alphabetically by whichever column you need. This was really handy during the build as I could easily switch between sorting by harness, numerical order, system, etc.
The remaining piece to the puzzle is knowing how to lay out the harness. The simplest method is to just start laying wires in the car from point A to B to get lengths, but I wanted to be able to build the harness out of the car and also have the plans so that everything is replicable in the future if necessary.
I took measurements on the car and then drew up the build plans:
Now, much of the above is a bit overkill. The key info there is the lengths between splits and the layout. The rest isn’t necessary but I like to be thorough – with this plus the connector diagrams that I show just a bit further down, I could build a matching replacement harness without any need to refer to the car or the original harness.
With the planning sorted it was time to start laying out the harness. I transferred the measurements to a 4’x8′ sheet of particle board with screws placed at each branch split for turning points. Progress shot with the chassis and tail wires being laid out:
The wires are labeled with their ID number on both ends. Here is where the thermal label printer got a workout:
All of the wires used are milspec /32 series with tin plating and very abrasion/temperature resistant insulation. This stuff is a big jump forward from standard cross-link OE wire in terms of durability and is also more conductive and lighter weight. It sounds obvious but the wire is the core of the car’s electonics and nothing else can make up for poor quality wire. IMO this isn’t the place to scrimp.
Most of the materials for this build came from ProwireUSA. Excellent source for professional/milspec wiring materials and the staff is very knowledgeable. They’re local to me but on the other side of town so I can attest to them doing a great job with order processing/shipping times as well.
With all the wires laid out the next step is looming things together. Time for some more materials! Here is all of the shrink tubing used in this build, in several various diameters.
Pictured:
Raychem RT-375; the clear stuff, for covering all the labels.
Raychem SCL; 3:1 shrink ratio, semi-rigid and adhesive lined for sealing bare crimps and also providing strain relief.
Raychem ATUM; massive 4:1 shrink ratio, adhesive lined and flexible
Deray V25; 2:1 shrink ratio, non-adhesive. This is similar to Raychem DR-25 but is a thinner (lighter) version designed specifically for motorsports.
Kapton tape (upper left); super high-heat resistant tape for wiring assembly. Serves as a barrier between the wires and the adhesive shrink tube so if you need to service the harness later you can cleanly cut the tube and tape off and you have like-new wire underneath.
Everything is tagged with its specs. You don’t want to accidentally use an adhesive lined tube where you don’t want it.
NOT pictured above is another loom material that I used in a lot of areas; resin infused braided fiberglass loom. It’s resistant to chemicals and can withstand a massive 1200° F. That’s quadruple what the good heat shrink tube can take, so this was my choice for the bulk of the chassis harness that runs along the trans tunnel and firewall. Overkill? Yep. I weighed the shrink tube vs. fiberglass loom and they are even, there’s no weight penalty for using either one over the other, except in cases of a run of just one or two wires where there is shrink tube available in smaller diameters than the smallest fiberglass loom. For wire runs of ¼” diameter and up it’s a wash.