1987 4 to 8 wiring

D.Piper said:

It seems like the swap is mostly complete, entire drivetrain is swapped, has the MAF plugged into the intake. The guy said that he tried doing a custom universal harness and had the car running but said it didn’t run right. I was wondering if I could take the harness from a 91 and use it in my 87?

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The wire colors won't match because there was a change implemented in 91 for the wire colors for some of the engine mounted sensors.

An 87 computer wiring harness with an add on Mass Air conversion would be your best bet.
The conversion harness seems to work well for most folks. It avoids the compatibility problems in using a harness from the junkyard. Simple and cheap, actually less work that swapping the wiring harness.
Conversion Harness kits & parts
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The note below said that the 91 computer harness is compatible, but I cannot verify that it is compatible.
Copied from bbunt302
Just for reference, here's a list of all the compatible years:

89 harness should work for 86-89 as long as you're using mass air.
90 harness will only work in a 90. (because of air bags and dual dash connectors)
91 through early 92 harnesses should be compatible (single dash connector, fuel pump relay under driver's seat)

Late 92 through 93 harnesses may be compatible (single dash connector, fuel pump relay under the hood). You may end up running some extra wire for the fuel pump relay. Comments and input from someone who has actually used the 92-93 EFI harness would be nice.