this is a continuation of a post coming from a similar question on an 89 wiring harness. I have an 86 coupe and have found an almost complete 88 engine wiring harness that is in really nice shape whereas my 86 is toast. I have been working on them side by side and have come up with a few differences and hence a few questions.
#1 just above the battery there are two relays, one for the fuel pump and according to the shop manual one for the trans overdrive. the connectors are different on the 86 than the 88. question is if there is any difference in the relays themselves. If not I can just buy new 88 relays and plug them in and use them in place of the 86 ones.
#2 the 88 harness that I bought had the harness lead down to the auto trans cut off but some of the wires were left. most of the wire colors match up and there is the same number of wires, but there is a yellow and blue wire in the 88 that are not in the 86. the blue may be a ground as the 4 prong connector on the 86 shows a cut wire sticking out of that color. the only wire on the 86 that is left is a brown with a white stripe. does anybody know if using this wire with the yellow will cause problems.
#3 the last issue is that on the 86 there are two connectors coming off what appear to be the right side and on the 88 there is only one connector with only 4 wires, wheres the 86 has one connector with 4 wires and one with 2 wires. they appear to go to the ac/heater box and may be different in that my 86 with two connectors has c86 electronic ac and the 88 with only one connector may have had manual ac. any help in how to change or modify this harness to work will be greatly appreciated.
merrillgtrs

 

I believe I mentioned earlier in another thread to post the part number or portion of the part number that will be found wrapped around the harness conduit near the bulk head connector. That would help a good bit. Post it for both harnesses or if you've more than two post them all.

 

the 86 has a black corrugated tape band and it looks like it had white writing at one time, but it is gone. the 88 has a clear tape with the numbers 7672 with kwo below it and 7672 with what looks like kwj below that. hope this helps. thanks

 

By part # that harness is an '87 with A4 and AC (doesn't matter C60 or C68) The '88 production was different but not covered in the FSM until a supplement was released. Could have that harness come from an '88? Don't know but I can assure you that when you start matching "pin-outs" the '87 FSM should match the harness.

The complete part # would have been: 12067672

 

GM changed the connectors (and relays) because the '86 connectors are not waterproof (that's why they put the black dielectric grease in the connectors). Those two relays are the MAF power and MAF burnoff relays. In '86 the relays were different. In later years they are the same. You can use the later relays without problems.

The fuel pump and (if you have a manual trans) overdrive relays are next to the windshield wiper motor.

There are two wires going to/from the trans. One is for the TCC (Torque Converter Clutch) lockup -- it goes FROM the ECM TO the trans. The other is the 4th gear switch -- it goes TO the ECM FROM the trans. It tells the ECM that you're in OD so it turns off the SHIFT light if you're going faster than 40 MPH. I don't know which color the wires are. I put an '89 700r4 in my '86 and the wiring did not change.