The 4 fires coming out of the fuel pump are black, black with a white line, green with black line and blue. Blue wire gets 8v and runs to dash for fuel gauge. Green w/blk line gets 12v when I turn the key but goes back to 0 when you let off the key. Black and white I’ve traced to the wiring harness by the fuse box and I assume it’s a ground but not 100% certain about that. Black I’m for sure is a ground. I bought the truck and it started stalling when I came to a stop. Thought it was the fuel pump so I replaced it and it ran for a bit but would still stall when stopped. Took it for a test drive to show a friend and it died and hasn’t started since. Fuel psi is very low like 3-4psi and it should be 35-45. I have 12v at the relay and the fuse they’re both good. Just trying to get this truck running again and not sure where to start.

 

You did already start doing the right tests, now figure out why the fuel pressure is low. I would try to power the fuel pump directly and see what the pressure is. If it's still low it's the pump (new doesn't mean good especially if it was cheap) or unlikely a clogged fuel line. If the pump builds full pressure the circuit in the vehicle can't carry the necessary current to drive the pump which points to a high resistance connection somewhere. Could be the relay itself, the power wire to the pump or the ground. Eliminate each component (jump the contacts in the fuse box, connect a temporary ground, connect temporary power but use the vehicle ground).

 

I ran direct power to the pump fuel pressure went up to 42psi truck still won’t start. Starting to think maybe it’s an injector blockage. Not sure yet.