I have a 1990 Ford F-250 diesel. I was wondering what years that the wiring harnesses will interchange from. Also will an international glow plug wiring harness plug into the ford wiring harness?

 

The glow plug harness from an S series should be the 7.3 style. 88-91 should be the same and 92-94 will be the same. They might all be the same post 87, but i think they changed it in 92

 

Also, remember that it really shouldn't matter what harness you use -- all that matters is your harness matches your GP type and your controller. Other than that, just make sure you get power to it, and you should be fine.