1985 CA F-250, 460 C.I. & 4 WD, with AC. Dual factory tanks.

My F-250 has begun blowing a fuse causing the truck to stall. According to the plastic fuse cover this fuse is “WRNG LPS” the Hayes manual labels this fuse “shift module, 4WD, and speedometer.” The fuse is a 15 Amp and is in the second position away from the flasher module.

When I replace this fuse in my driveway and remove it the truck will run out of gas in a minute or two. I suspect this fuse is for the fuel pumps. Toggling between tanks does not do anything. The tank selector solenoid is on a separate circuit. In my driveway this circuit draws 350 MA with the key in the on position and 550 MA with the truck running. I am unable to determine what else might be on this circuit.

At any rate this fuse blows in a totally random fashion. So far always when driving. Nothing has been added or changed on the truck.

I inspected the wires as best I could all the way from the firewall, along the frame rails and up to the fuel tanks. I moved wires away from metal.

Just to see how bad the issue is I installed a 25 Amp fuse and it blew as well. But only after a random on road driving period, and remember the circuit draws less than an amp in my driveway.

Could the fuel pump be intermittently bad and causing this? What other devices might be on this circuit causing this? The heater/AC fan is on a separate circuit as is the tank solenoid.

Any help or suggestions are welcome.

Regards,

BigJim