Wiring on a 5.0 change over?

It's on a 94 Mustang. The harness is from a 90 model.

You'll get it to work just about as easily as mating a wildcat with a pit bull...

The 90 Mustang harness only works with a 90 Mustang. Get a 94 harness form one of the online junkyards if there isn't one in your area.