I am in the process of removing my engine and auto tranny and swaping in a j-spec turbocharged + manual tranny. My ecu that I have is a N351 I know I have to install a N374 ecu, pressure sensor and MAF,etc. What I wanna know is can I use my wire harness (N351) on a N374 ecu or do I have to change the whole harness and fuse box and etc ? Both engines and trannys are S5 btw.

 

You should use the an S5 turbo harness for the motor with the turbo ECU...

you MAY have to re-pin the body harness where it plugs into the ECU though, I am not sure if they are the same (and would assume not given the difference in gauges between turbo and non)

It is may be possible to repin your non-turbo harness to run the TII ECU and motor, however this (if possible) would be a very involved job.