89 is when harness changes happened, as far as conectors.  I think either 90 or 91 they went to a two plug ecu instead of the earlier three plug.  The harness from the 94 shoud work on the 90 engine, i don't think much changed.  Also, the harnesses from 89 and later are mostly stand alone, so there is alot less of the dash stuff to worry about.  In fact, the ecu to engine harness is all by itself, then connectors come of that to go up into the dash.  The main thing is that the harness and ecu match.