kinda already know the answer, but its worth asking
 

im buying a s5 jspec motor, and so i plan on selling my stock s4 turbo wireing harness and ecu, and i already know all i need to replace is the "engine harness" or the one with all the connectors on it comming through the firewall on the pass. side. but my question is, do i have to pull the dash to get the harness out?
i really dont want too, considering i just put a new heater core, ac thingie and blower fan in like two weeks ago and when i put it back on, i put everything on. every last single fucking bolt!!

If you are putting this into an S4 car, save yourself some serious hassle and just use the S4 electronics to run the S5 engine.

However, if you go the hard route, no, you don't need to remove the dash to remove the engine harness.

would i have to change alot of connectors and mumbo jumbo to do what you speak of?

come on guys

I would think that the harness not only does just the injectors and sensors, but other shit coming from inside the engine and crap. Basically alot more connectors than you might be thinking. Its just a shitload of work, but im prepared to do it, it would be nice to know where everything hooks up to, so if I do it, then I'll know.

Yes.
All of the harnesses that plug into the ECU and the ECU unit itself would have to be changed over. Those harnesses snake through the entire dash assembly.

Why not just run your S5 Jspec engine with your S4 ecu and keep your S4 TII injectiors, Throttle body, etc?

eh, my s4 stuff is running on 133,000 miles, the injectors would no doubt have to be cleaned, the intake mans are in good cond. but the tb is kinda sticky.
id be alright if i didnt have to keep too much i guess.

Pretty much all the electronics, the TB, and if you don't want to premix, your front cover and metering oil pump will have to be kept.

I have only just found this out, I was putting S5 in my S4 and never gave all the wiring a thought until the other day. I am now trying to sorce S4 electrics and stuff so I can get it running. I have really kicked myself!

i have all the stuff from my s4 motor, but wouldnt it be easer just to buy a s5 ecu and wireing harness? considering i can just sell my old one for the about the same price to some N/A guy, and the motor im getting is a long block with 44,000 miles on it anyways

I think what others are saying is that it is more than just the ecu and ecu harness, theres the wiring under the dash to consider. i went out side to my car and realised that the S5 ecu DOES NOT plug into the harness that leads somewhere into the dash. Im not to sure on what wires are what in the dash, but theres lots to consider.

Im taking the advise from the others and are using the core and turbo etc and running the S4 ecu.
My 2 cents

i was always under the impression that it was just the right side wireing harness, and that the left side pluged right in.

Yeah so was i, until a read a thread the other day!

do share a link please :)