fuel gauge woes

[hatzie]

Stock 73 should have a DPDT on-on switch with 5 wires. Half of the switch controls which sender is routed to the gauge through one side of the switch. The other half of the switch sends power to the solenoid valve when the auxiliary tank is selected.

A DPDT on-on toggle with a six contact arrangement could be installed as a direct replacement for the rocker switch by clipping the unnecessary lug.
Assuming the PO didnt butcher it too badly in an attempted repair or attempted update to the later motorized valve... Unplug the switch. Ground the center terminal on the side of the plug with three wires. This should peg the fuel gauge when the ignition is on... if the wire is intact from the gauge to the switch.