It should.
The 87-88 L4 ECM's are all 1227748. The PROM and some wiring to the ECM is differant depending what tranny is in the car. Specifically, the wire that runs the shift light in a manual car runs the TC lockup in an automatic. The Auto ECM wiring also gets at least one signal from the auto's neutral safety switch.
The Whole engine bay (500 zone) harness would need changing. There are interior changes you may also need to make. Since you apparently have the entire 88 harness I'd take the whole thing.
I don't know exactly how much interior differance there is. GM has a habbit of jumping and/or hiding plugs you don't need for certain options. Just for safety... I'd take the entire 200 zone, that's almost everything from C100 (front compartment interface) back. That will give you all the TC lockup wiring from the brake pedal and so on. It's a good chunk more work but it would eliminate splicing and dicing to make any needed changes.
Note: the 300 zone "cross car" harness doesn't need to be changed unless the 88 has door options you want... Power Windows, locks, mirrors, etc. (Wire Zones are explained in the wire reading article in my cave.)
extracting and installing wire harness is more time consuming than difficult. (I've done it on far bigger things than Fiero.) If you think you might forget stuff use a digi cam and/or tag stuff as you take it appart. Most connectors only fit one way and one place so it's not rocket science by any means. (The car makers all do that on purpose. It means the average git on the assembly line can't screw it up.)
------------------
RIP Crew of Columbia. 01-Feb-03
