What exactly do you mean PCM?? And what is the big terminal? Please help I just got this truck and now it won’t start a glow plug Relay gets really hotThat's because the relay is closed. Try unhooking the two small leads and try the big terminal again. If you don't get sparking, the relay is good, and the problem is the small leads. One of the small leads gets positive feed when the key is on, so that wouldn't be the problem. The other gets grounded by the PCM when it wants the relay closed. That would be the wire that would be grounding out somewhere.