*dusts cobwebs from old obd1 memories* If I'm recalling correctly, the fuel pump gets triggered from ecm when you turn the key on for approximately 2 seconds. Then the ecm waits for notification that the engine is running. This occurs by 2 methods. 1- crank sensor indicating engine turning, or 2- presence of oil pressure via oil pressure sensor.
Crank sensors can go bad, but it'll still run because of the secondary oil pressure sensor backup.
The fuel pump won't be running all the time the key is on. That makes one-man diagnostics a bit difficult. My personal trick is to remove fuel pump relay and place jumper wire between hot wire and load wire, thereby sending power to the pump. If the pump does not operate in this scenario, you have constant current being supplied to the pump, and you can then check if you have power to the pump.
These trucks are getting older, and on my 94, I just had a tail light issue that turned out to be a broken wire in the harness under the cab. I jammed a long extension between brake pedal and seat, grabbed test light, probed wire until I found the dead area.
I hope this gives you some ideas!
