There are at least two gauges that share a common path. Power comes from the key, goes to the "voltage limiter" (inside the fuel gauge on some cars, a separate component on others) and the voltage is dropped to a pulsing 12V approximately the equivalent of 5V or so
THIS lower/ pulsing voltage feeds the fuel, the temp, and the oil gauge if you have one
From there each gauge goes to it's own sender to ground.
Some of the troubles popping up lately:
First of course, is the pins on the cluster connector. These become loose and corroded, so the gauges may not be getting power
Then 'is the instrument regulator/ voltage limiter' working?
(If the opposing gauge (temp) is working, at least you know the gauge power to the limiter is OK, and the limiter is working.)
These (limiters) can go bad, as well as lose contact. On my old 67, originally, the spring contacts which the limiter plugs into were not actually making contact with the PC board. I saw in a photo just yesterday on here, that someone making repop boards solders these to the board. I already did so on mine
Also, the nuts for the gauges may be loose/ corroded where they make contact with the board, and of course
the pin on the board connector for the sender may be loose as previously mentioned
and you may have a corroded connector or broken wire.
Once again, does you other gauge work?
In any case, it's time to pull the cluster. Not that difficult. Drop the steering column and get to it.
