4cyl. to a 5.0 swap

[Coolbreeze]

Yea, I call it the main harness; the one from the EEC to the engine compartment. You won't have to mess with any of the dash stuff unless you try using different years harnesses. I.E.. an 87-89 will need an 87-89 v8 harness and the 90 harness looks like the 89 but won't work without some re-wiring and the 91+ are different. The 91+ only have one plug(redish brown) compared to the 2(black & grey) the 87-90's over where they plug into the dash harness behind the driver side stut tower.

But you should be OK using the 89 harness in the 89 car...We used an 89 harness in an 87LX when we did my buddies car. We tried a 90 and the fuel pump wouldn't come on. They say it can be made to work but no one has said how to re-wire it to make it work.