How does a 1987 F150 switch between fuel tanks?

A 1987 Ford F-150's fuel tank selector switch operates using a simple rotary switch located typically near the instrument panel or the center console. This switch electrically controls a valve that directs fuel flow from either the main tank or the auxiliary tank (if equipped with two).

The process is purely mechanical: Turning the switch changes the position of the valve, selecting which tank's fuel pump receives power and thus which tank feeds the engine. There's no sophisticated computer control involved. If you have a problem switching tanks, the issue likely lies within the switch itself, the wiring to the switch, or the valve mechanism in the fuel system.