Need help solving my problem with my double gas tanks on mu 1981 F100. The back tank will feed the gas to the engine but the front tank will not feed the engine when I switch to that tank. I have gas in the tank. Please help.
The rear tank is default on the selector valve solenoid located on the Drivers side inner frame rail. It's means of ground is where it attaches to the frame. There should be one brown/white stripe wire feeding into it.
With the tank selector switch in the dash switched to Front, you should be getting power to this wire at the selector solenoid. Use a test lamp, with the ignition switch placed in run with the engine off. If power at the Brown/White stripe wire, try cleaning the ground to the solenoid by unbolting it from the frame and using sand paper to make metal to metal contact, then reattach the solenoid. You can use dielectric grease to help fight future rust issues where the solenoid and frame connect.
If you have power at the Brown/white stripe wire, and cleaning the solenoid contact to the frame doesn't work, you most likely need a new Fuel Tank selector solenoid.