1995 Ford F- 150 Gas Gauge

Could be the gauge mechanism, a loose connection between the gauge movement and the flexible printed circuit board of the gauge cluster, the gauge voltage regulator (somewhere in the cluster), the gauge cluster to wiring harness multi-connector, the tank selector switch on the dash, or a grounding issue with both tanks.

The only way both gauge senders could fail at once past the selector switch is if they are in a common wiring harness, a connector comes unplugged, and they both go open at the same time.

The gauge voltage regulator is a long shot, because that would probably knock out the oil pressure and temp gauges also. (Unless it has a separate voltage regulator for each gauge, possible but unlikely.) You said the other gauges were working properly.

You may have to do this the hard way - get an ohmmeter and trace the wires from the tank senders forward, and find the open.

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