alrite. Lets say you want to do an S5 TII conversion. Is it necessary to have all the complementary S5 parts (Ecu/ Transmission/ harness/driveshaft/diff) or are they interchangable with S4 TII parts? Let me know - I'm still learning/gathering information. Thanks in advance.

The trans are the same the rear diffs have two differant types of lsd's but either would work for you, personally I like the clutch type s4 but the s5 doesn't require as much attention.

The ecu's are differant. Won't say about the harness because I really don't know.

I am currently working on a TII swap in an 86. Thus far, I have everything from the transmission back swapped out for that of an 88 10th Anniversary. No issues so far.

I am looking at possibly redoing all the wiring. With a Haltech Computer. But I am not sure.

wiring is alot different but you can match up the wires and stuff, but i dont know why youd want to