Dieting the Chassis Harness

[grathke]

I have a question about using the stock subaru harness. I know there is quite a bit of talk about dieting the harness and remove a ton of wire, but was thinking of approaching this differently.

What about keeping the harness in the same approximate orientation where the ecu would be at the inside of the front firewall, the headlight and front turn signals would be up there without needing to extend them (or at least not much). Then either extend the factory ecu harness to the engine in the rear, or purchase an extension for that harness. If you take this approach wouldn't most connectors, and switches be in their approximate location without having to pare it down?

Has anyone considered or done that? Any thoughts? Perhaps this is too simplistic of an approach, don't know enough about this yet.

Thanks
Glenn

[Hindsight]

I did exactly that. You can check it in my build thread. I mounted the fuse/relay boxes under the dash, to the frame, facing down so if you put your head under the dash on the passenger side, you'll have access to the fuses and relays. My ECU is bolted to the cabin side of the rear firewall that goes over the passenger side portion of the fuel tank, and then I built a removable cover that covers them. I had to extend and shorten a lot of wires. This is different than dieting. Dieting is when you remove wires for crap you don't need like the sunroof, radio, power locks, power windows, defrost... the list goes on and on.

I can't say if I had to extend or shorten more wires than people who did it a different way, or whether orienting the harness like this was less work than following FFR's suggestion but every single wire in my harness has a splice in it that was soldered and covered in dual-wall 3:1 heat shrink.

[grathke]

Thanks for the reply, I will be sure to check it out.

[STiPWRD]

I can only recall of one build where they put the ECU under the dash, so it has been done:
http://s957.photobucket.com/user/nancarrowa/media/IMG_1454_zpsc9734cfa.jpg.html
http://thefactoryfiveforum.com/showthread.php?16406-AJW-Performance-818-Donors-818-S-For-Sale

One of the reasons many don't take this approach is because it involves running many wires from the ECU to the engine along the center tunnel. This is an area which is limited on space for all those wires. Once you diet a stock subaru harness and lay it in the 818, you'll quickly see what I'm talking about.

[mistasherm]

I am at about 95% from having my dieted harness fully installed. I placed the ECU on the rear firewall for the reason(s) that STiPWRD mentioned. It started out as a very intimidating pile of wires but it is now a very manageable layout that required some wire adjustments but no more than would be required if you placed it under the dash. As mentioned, you will have quite a bit of wire occupying the center tunnel running back to engine. I removed about 15lbs. of wire and bits from my harness. By placing the ECU on the rear firewall you are really just turning the entire harness set-up about 90deg. from it's original orientation in the donor. So the wires that you are worried about lengthening (headlights, turns sigs, etc.) are actually still in the right position.

[Hindsight]

Looks like I misread a part of your post. I only put the fuse-boxes up front under the dash. I mounted the ECU more or less near the position FFR advises. It's easier that way and less wires.

[Harley818]

I did the same basic method as Hindsight for the same reason. I didn't want to compromise the engine wiring harness, and I could still have the ECU on the cockpit side of the firewall I added, and I have the main fuse relay and fuse blocks near the front. However, the only wires I needed to lengthen were the alternator wires, and the lights to the front (maybe back as well).
I only had one wiring problem..... just discovered last week when doing my dyno. No connection to injector 1.