I’m new here (first post). You would think this has been asked a million times but I’ve searched everywhere and not found any thread that has done this exact swap. I’ve got an 87 4 cyl 2.3 auto convertible that my dad bought new. I bought a 93 GT T5 hatch to swap. I knew this wasn’t the ideal year to buy but it was available and it was reasonably priced. I also have a friend that parts a lot of mustangs and he’s got a couple 89’s. I grabbed an 89 ECU harness from him (I have the 93 A9L) I’m also getting the forward light harness (for the alternator connection) and the O2 harness. I can get pretty much any of the other 89 harnesses if need be. I know that the MAF housing and sensor should be from an 89 and I can’t use the 93. My plan is to only use the 93 engine and engine harness if possible but if any of the other harnesses work from the 93 (clutch, tranny, etc) I’ll probably use those too. From everything I’ve read this should work. I’m just looking for a little guidance for anything I’ve missed.
The 89 harness would be the best swap, or use everything from the 93, including the dash wiring with the instrument cluster, you have everything in the 93 you need just ignore the air bag stuff.
It's a major job but been done before.