1986 Ford F-150 Fuel Pump

Electrical problem
1986 Ford F150 V8 Four Wheel Drive Manual? Miles

my high pressure fuel pump under the driverside door works but its not getting power to it for some reason. I traced the wires back and it seems to go into my firewall. Not really sure were to go from here. Also when I tried to start it the gauge in the dash drops from showing the actual gas thats left to all the way to empty if I keep trying to start it. Not sure if this has anything to do with it. The truck stalled on me one day and I wasn't able to start it. I've been able to start it twice in the past month just randomly. But not for a while. Thanks for any help.