The fuel pump is continuously priming. We have a '88 F-250 that has the same ECM and relays. I've switched out the ECMs and relays to test them. The ECM and relays work properly on the truck but when I move it back to the 'stang it still continuously primes. Anyone have any ideas?

 

The car is a 1967 Mustang with an '89 Foxbody 5.0 Cobra engine and all the wiring is '89 Foxbody original wiring, if any of that makes a difference.

 

There is an old checklist from stangnet you should work your way through.

https://www.stangnet.com/mustang-for...engine.773003/