Hello all.
So a s4 FC (n/a) roller showed up 4 years ago, it sat parked in my garage whilst I kicked around the idea of an LS swap, a 2jz swap, even an electric swap. I finally landed on a turbo II swap and now there is a '91 JDM turbo II engine/trans on a hoist in my garage. My goal is to use as much of the stock equipment as possible to stay within budget and simplicity.
I've spent a good amount of time learning what I'm still missing, where it goes, and where it connects. The Hanyes manual only gets me so far, as I'm finding (and expecting) slight variations betwixt US and JDM setups when it comes to both mechanical and electrical components.
The engine came to me with the ECU and partial harness. From what I can tell, and from many hours on the interwebs, I seem to be missing the part of the harness out of the ECU that controls/ connects both sets of leading and trailing coils, ignition switch, and main power/ relay among other things. This would be the medium sized 22 pin connector at the far right side of the ECU.
My thinking is that maybe this part of the harness was loomed into the chassis electrical (headlight motors, relays and such) and thus was not removed from the donor.
If anyone has any incite or experience with this part of wiring, I'd greatly appreciate tips on where to find or how to assembly a harness possibly using the n/a wiring that is still in the car.

 

Being that it's 2026, and we have much MUCH better modern ECU and injector options, I would highly suggest you take the plunge and go standalone. I know the cost can be a limiter, but these engines are getting harder and harder to find, and blowing them up on less than ideal factory computers and questionable 35+ year old wiring harnesses is a gamble in itself. Since you already need to redo a wiring harness, is making a new one from scratch to run a haltech 1500 or Link an option for you? I think in the long run you'd be happier and have more peace of mind that its not questionable.

 

the coils, ignition switch and all that other stuff are on the body harness, assuming its still there. the S4's vary a lot, between NA, Turbo, and JDM, the S5 stuff is more the same between models/markets so if you need something S5 is easier.