How does this work? Many wiring questions!

[Clyde's Keeper]

It's not clear to me, many things are not clear yet but that's another story, what happens to all of the extra wiring that is not needed? How does the engine management system work with some of the systems disconnected. It seems to me that the check engine light would be on for many reasons including but not limited to disconnecting the evaporative system. Also seems like you would get ABS and air bag warnings due to disconnected devices and sensors. On my current build, due to budget, I am committed to using the stock wiring, seems a little daunting.
As I am always thinking of future builds, just wondering what other options there are for wiring. I made the wiring harness in my MKIII roadster with a kit from then named?? I Squared. Very simple, straight forward and no unneeded items, but my roadster has no engine management/computers. The WRX engine needs at least some sort of basic computer to get it to run.

I hope my questions are clear or clear enough, my head is sure unclear.

Thanks,

Robert.

[STiPWRD]

Hi Robert, you may want to start by downloading the wiring manual for whatever year donor you have. I used an 02 wrx donor with stock ECU and dieted all of the stock wiring so I think this is along the lines of what you're after, right? What year is your donor? And let me mention that I knew very little about Subaru wiring before I started so anyone can learn with a bit of time and research.

To answer some of your questions:
1. All of the old wiring I cut off was put into a box and I often went back to recycle this wiring for extending parts of the harness or adding new wiring. It helped me maintain the correct colors when extending wiring, which really helps when troubleshooting. I cut off over 20 lbs of wiring.
2. The engine management (ECU) isn't connected to every single bit of wiring on the car. For instance you can delete many systems like door wiring, stereo, airbag wiring since the ECU is not directly tied into these systems. The ECU is mainly concerned with things attached to the engine.
3. I deleted my ABS system and airbag system and don't have any lights. If you do get a light, it can usually be easily fixed by simple changes to the gauge cluster wiring.

[redfogo]

It's not clear to me, many things are not clear yet but that's another story, what happens to all of the extra wiring that is not needed? How does the engine management system work with some of the systems disconnected. It seems to me that the check engine light would be on for many reasons including but not limited to disconnecting the evaporative system. Also seems like you would get ABS and air bag warnings due to disconnected devices and sensors. On my current build, due to budget, I am committed to using the stock wiring, seems a little daunting.
As I am always thinking of future builds, just wondering what other options there are for wiring. I made the wiring harness in my MKIII roadster with a kit from then named?? I Squared. Very simple, straight forward and no unneeded items, but my roadster has no engine management/computers. The WRX engine needs at least some sort of basic computer to get it to run.

I hope my questions are clear or clear enough, my head is sure unclear.

Thanks,

Robert.

This thread I made might help you http://thefactoryfiveforum.com/showthread.php?21030-DIY-ODBII-working-standalone-wiring-harness

I deleted just about everything you can think of. The big things you need to make the car start and the ECU happy to run is Fuel pump, ignition, and main relay. If you got all those 3 relays in and everything that connects to them plugged in car should be happy.

[Clyde's Keeper]

I feel better already!

[AZPete]

Robert, I also built a roadster with I-Squared wiring and now have an 818C with dieted donor wiring. I'm a dummy on electrical stuff but it can be done if you are careful. This thread by Mechie3 was a savior in identifying the details of the donor harnesses.
http://thefactoryfiveforum.com/showthread.php?11880-Wiring-Guide-06-WRX-Sedan-with-Auto-AC-HVAC

I-Squared morphed into Infinity so you can use it in your 818. Also, iWire has simplified the wiring and I would have bought it if they had existed 3 years ago when I started my 818S. The wiring gurus on this forum have figured out how to disable the instrument panel lights. Some of us (the lunatic fringe) are using the donor ABS, power steering, cruise control, and some other features of the donor but cut out other stuff like air bags and door dingers. You built a roadster so you can jump into the 818 pool. The lifeguards are here and they saved me many times.