FSM should tell ya where the wire goes. Id try to get a plug form a junkyard to make it plug and play...
But an off the cuff guess is the wire may alreayd be int he plug - just not in the harness.
In the WORST case - you'll have to use a "eye" crimp ocnnector tothe back ot he "bolt" that holds the tach to teh cluser/trace (what it looks like on th e85-88 ones anyway)