I have just read through this thread and am even more confused than ever! I was thinking about doing this same swap on my S4 to an S5 motor. I will have the harness, ecu, EVERYTHING at my disposal from the S5. Why can't I just swap all of these items and call it a day? Why is there all of this about swapping my cruddy S4 stuff into this perfectly running S5 motor? I see all of this modifying and whatever but it just seems like such unnecessary headache that could easily be avoided. Someone clear this issue up with me.

 

Please, any help would be appreciated. I even used the search function for this!