I have a 1989 F-150 5.0 EFI that has a bad motor and i would like to put a 5.0 EFI that came out of a 91 F-150 in the truck. both trucks are auto and 4x4. I am trying to figure out if i can use the wiring harness out of the 89 and what other problems i will run into during the swap. i would appreciate any insight.

 

Yes you should use the engine harness from the '89 and also the '89 flexplate or flywheel.. do not assume they are the same, this should be a direct swap otherwise.