Fuel gauge limiter
The winding inside the fuel gauge may be burned in two or maybe just a bad connection where the gauge is attached to the printed circuit board.
the 2 nut/bolts holding the guage to the circuit board were corroded..
^^ THE ABOVE ^^
I've preached and preached this. Think of the gauges as "an end to end system."
That means all the way from one battery post, in the long circuitous path back to the other battery post, all the wiring, connections, components in between. EVERY single one
The list of "what was wrong" on my 67 is lengthy. ALL of this was "wrong" and "each" one would have rendered the gauges inoperative:
1....On a side note, due to "the usual suspects" there was voltage drop in the bulkhead / ignition circuit. READ
http://www.madelectrical.com/electricaltech/amp-gauges.shtml
2....The pins on the (two) PC boards connectors were loose and broken
3....The limiter SOCKET in the board....springy contacts which are pressed into the board....were not making contact with the board traces.....I soldered jumpers across
4....The limiter was bad
5....THE NUTS ON THE GAUGE STUDS were corroded and NOT MAKING CONTACT between the gauge studs and the gauges.
NOT a factor in my car, but possibilities in other cars:
6.....Any bad connection in the sender circuit, IE in the bulkhead or kick panel, or the sender end connector itself
7.....Obviously, a bad sender. Corroded, sticking, sunk float, physical damage due to collision, on and on
8.....Improperly or poorly grounded sender due to corrosion at the tank to body
9....A bad / worn out / sticky / burned up gauge unit. Let's not forget how old these are, and the environments some of them "have been through".......very hot unrelenting AZ and TX and CA sun, or sub freezing temperatures, or saturated humidity and rust, corrosion OR ALL OF THESE for the last 45 years!!! LOL