Try these links.
Fuel Gauge Testing The Filling Station
Gas Gauge Problems fifth ave internet garage.com
Connect +6V to the gauge power terminal. Connect the battery negative or ground lead to the gauge mounting plate. At this point, the gauge needle should go to "full" or beyond. Now connect the gauge sender terminal to ground (or the mounting plate). The needle should go to "empty" or beyond.
The above test will show whether the dash unit is working or not. For an accuracy check, you will need a calibrated variable resistor or a tank unit
Picture Schematic wiring diagram for the fuel level gauge.
