1997 engine in a 1992 FD ECU differences
 

So I just swapped in either a 1996 or 1997 JDM 13b into my 1992 JDM FD. The harness from my old motor had 4 yellow plugs that plugged into the ECU, but the new motor doesn't. Instead it only has 2 of the yellow plugs and then 2 white, fat plugs. From the searching I've done so far, the newer engines did have fatter grey/white plugs for the ECU, but what I'm confused about is why does the new harness have 2 of the old style yellow plugs, and 2 of the newer style plugs? Everything I've found online has showed it should just be one or the other (4 yellow or 4 fat grey/white)

The two yellow plugs could be from the wiring harneess inside the cabin and the two white plugs are probably from the new engine's wiring harness.

Traced the wires back and yep, the two yellow ones are from inside the car. So my next question: what do I do? Is it as simple as cutting the plugs off my old harness then splicing them onto my new harness? Or will I have to completely change out the harness?

92 cars have 4 yellow plugs going into the ecu, 2 coming from the engine, 2 from the front harness. If it is actually a 96 on - pic would help! - newer ecu only takes 3 plugs, 1 left vacant....sounds like something doesn't add up....unless a splice job.

Install the S6 engine harness and solenoid rack on the S7 engine.

use your original engine harness. remove the newer white plug harness and use your original yellow plug harness and everything will be the same as before. the difference between is more than just wiring. the ecus themselves are completely different. also, just like banzai said, if youre keeping the rats nest then you will need to swap that over as well.

Is there a write-up on how to change out the harness and rats nest anywhere? I've tried searching but all I keep finding are LS swap harnesses and FC harnesses.

having a basic mechanical ability is all the write up you need. its not difficult. once you start taking it apart youll know what to do.