the speed sensor is a 2 wire hookup and dont think is polarity sensative. is it a factory harness or aftermarket. ? my sister lives about 10 min from me and has a 91 tpi /speed density z28 and i can help you with any unidentified plugs if its a factory harness. and somewhere i have the paperwork from my painless tpi /speed density harness .i just need to find it.