Q: fuel pump gauge on 1994 GMC Rally Wagon 2500

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Trying to figure ways to test the fuel pump gauge. It falls in front off the full icon and doesnt move at all Doesnt twitch apon start up,,,nothing. Is there a relay? Not fuse I that I know of.. Fuel pump assembly maybe or bad ground?? Im a girl just trying to be direct with my search, first time working on a van:) Also I hooked up an after market radio and it plays but gets really hot.. crossed wire huh? no static on connection of the speakers... Fuses are fine. No original harness.
(1) Answer
you need to find the wire back at the tank unit that controls fuel guage. with the wires unhooked, the guage will swing either full or empty. then grund the wire and just the wire for the guage. it should swong the guage the other way. if it does, then your dash unit is ok and your problem is in the tank unit.