Okay here's the background, got a rebuilt s4 tii drivetrain and everything that's been running in my s5 coupe for the last few years. When I swapped I just gutted both cars and dumped ALL the s4 stuff in the s5 including all the wiring. Well now I have an s5 vert that's gonna get the same treatment but I have a few questions/ideas that I'm looking for some info and feedback on. Do I swap all the wiring again and custom rewire the vert top components or do i find a way to make the s4 ecu and harness integrate into the s5 car and wiring. Now I am aware that I could take the time and money to source all the s5 turbo conversion parts required to have an s4 keg running s5 sensors and ecu, but I am by no means looking to spend that kind of money. Between s5 tii ecu, maf, boost, tps, and front cover with omp that actually works seems ludicrous. So what's everyone think?

 

If you want to use the S4 ECU & sensors, you get to adapt an S4 emissions (EM) harness into the car (the one connected to all the important engine stuff). Barely anything is the same between series, so wires will need to be cut and rearranged between the EM harness and the S5 front (F) harness. The S5 front harness ECU plug won't match the S4 ECU, so it has to be cut off and replaced with an S4 version. You're basically looking at re-pinning about 3 different harness junctions. I don't think the top wiring gets affected if you go this route.

If you were to replace the S5 EM, F and E (engine) harnesses with S4 versions, you'd still be looking at a lot of rewiring. And in this case, the top controls would almost certainly be affected, along with many other things. The first way I mentioned I think would be the "easiest", but both ways will mean studying both S4 and S5 wiring diagrams in depth.

 

Thanks for the input. I got into the car some and it's already missing all the harness except the em and door harnesses so that may be my deciding factor unless I can source the vert harness cheap enough. I already have the s4 wiring diagrams pretty much memorized from quite a few previous endevoirs with them and a good deal of the s5 coupe wiring. Not really afraid of any of that or putting in the time (I'm an auto tech by trade for the last ten years or so plus my pops is an electrician). I just feel a little bad about replacing s5 stuff with s4 but i'll have to do whatevers necessary cause I'd rather rewire and spend time then money (gee that sounds like a typical fc owner huh?).

 

I think it would be easier to dump all the s4 electronics in and then rewire the top.

 

Walken that does appear to be what I'm gonna do. There aren't enough advantages to converting to s5 ECM and whatnot to out weight the cost. Besides I hope to eventually dump the stock ECM for something better like a haltech. My only remaining concern is *if* I ever decide to part ways with it it may make selling it a bit harder. Guess I'll either have to be buried in it or find the "right" buyer.