Making new wiring harness from scratch, need help

[Dave W]

Jimmi
I did exactly as you want to do using a AE86. The build process should include spending about 20 hours making a complete vehicle schematic with color coded wiring call outs to assist in the construction of a new wiring harness. A complete wiring schematic will save more time, then it takes to make it, Vs trying to figure out which wires are which after having been away from the build for a week or two. I made my wiring diagram by enlarging copies of the Toyota AE86 wiring schematic and then cutting out the ECU and other circuit sections and pasting them on to a 20” x 30” sheet, before drawing in the connecting wires with color codes indicated on the schematic. There is more then enough wire length in the stock harness to allow you to use 90% of the same color codes and wire gauges from the Toyota GTS. Using the Toyota color codes make the designing, drawing, and fabrication of the schematic a lot easier. It also will make system trouble shooting electrical components a lot easier. Do not be surprised if a few of the Toyota wiring schematic color codes does not match exactly what is in your EA86. Toyota seems to have changed a few color codes each year and also in between model years, but 90 to 95% of the wires should match the Toyota schematic. You need to label all of your electrical connectors during the disassembly process. Then re-labeled or number them as you separate them and lay out the wires in the building process. As a side note, I tried to just remove the wires not need in the build. After spending 25 to 30 hours pulling wires out of the original harness and only maybe only 40% through the process I decided it was time to make a new harness from scratch. As far as the actual wiring, scrap the Toyota grounding relays in the AE86 harness and go to direct grounding of gauges and switches for a race car. I would suggest you add wiring for a electrical radiator fan. Depending on how confident you feel about your wiring skills, I would suggest that you just use the Toyota engine bay harness and make a one off harness for the rest of the vehicle. Scrap the two large junction blocks in each foot well of an AE86 and the miles of wire used to run the wiring from the RHD design over to the other side of the vehicle to make it LH drive vehicle. I save over 8½ lbs just in the wire not counting all the extra relays, junctions, and switches deleted during the simplification of the wiring system. Probably the easiest wiring approach is to use the Toyota engine bay fuse box and add a 2nd auxiliary fuse box for the dash and any added items. You will probably need to add a small fuse box with a minimum of 4-6 additional fuses. I have found that rubber trailer wiring harness junctions are very useful for both the front and rear end light connections of the wiring harness, This will allow for a quick disconnect during build and maintenance plus it is water tight connection. I would also add a few spare wires in the harness runs to both the front and back of the car. You need to spend extra time in the planning stage in the routing of your wiring. The best advice I can give is to isolate each circuit and either number or label your wire runs. If there is an electronic shop close by, stop in and purchase a few sheets of the industrial wiring stick–on numbers and/or letters. Cut and apply them to both ends of each wire run that is installed when using wires that do not have a color code i.e. plain aftermarket wire. [Mark these numbers or letters on your schematic]. Time wise it is quicker putting the harness together and the appearance will be much better and orderly. While stringing out each individual wire in the harness, using Velcro tie warp will make it much easier to add each new wire to the harness run. Once you have assembled all the wiring then you can come back and install permanent “P” clips mounts on the frame aand body. I used plastic “P” clip that have a latch design that allow one to reopen the clip, if at a later date you want to add or delete a wire. When checking your completed circuits, start by installing each fuse one at a time. Once you have verified all the circuits, then go back and rap the harness with wiring split tube or plastic spiral rap and attach it to the frame with “P” clips. I would not use tape to wrap the wiring harness, because it will be PITA to trace or change any of the wires. I also solder about 90% of all my connector, but if you go that route, you do not need but a drop of solder on each connector. Last you can never have to many grounds connections. Plan on about 50 to 60 hours to complete the task. Dave W