The fuel gauge selector switch is a momentarily-closed-type switch located on the vehicle dash. Contained within the fuel gauge selector switch is a fuel indicator lamp (FIL). The fuel gauge selector switch allows the operator to check the fuel level of either fuel tank-regardless of which fuel system is operating. The AF ECU monitors the state of the fuel gauge select switch input circuit. When the fuel gauge selector switch is depressed the AF ECU responds by operating the fuel gauge relay. Operation of the fuel gauge relay determines which fuel tank level signal is received by the fuel gauge in the instrument panel. The fuel gauge will display the NON-OPERATING fuel system's fuel level for about ten seconds after the fuel gauge selector switch has been depressed. Passenger vehicles have a filtered fuel level display, depress the fuel gauge select switch 30 seconds after the vehicle speed sensor indicates the vehicle is at rest in order to avoid inaccurate gauge displays.

The fuel indicator lamp (FIL) is contained within the fuel gauge selector switch button. The fuel indicator lamp indicates which fuel system is in operation. The AF ECU controls the operation of the fuel indicator lamp. The fuel indicator lamp illuminates ONLY when the engine is operating on gasoline. The fuel indicator lamp will also illuminate for several seconds during start-up as a bulb check.