Originally Posted by RichardV6
I note you have a proper ground connection to sender. Many vehicles of that era had OE only the one sender connection, relying on tank to chassis grounding through fixings to complete the circuit.

With the moving iron gauge you almost certainly have a check on the instrument itself is achieved by simply removing the connection to sender. With ignition on the gauge should read instantly beyond full, and similarly with same removed wire touched to tank, the gauge should read below empty. This latter check also proves the aforementioned tank to chassis connectivity.

Thanks Richard. The previous owner rewired the car, including adding the grounding wires where appropriate. When I did the checks before refitting the instrument, the needle disappeared beyond full when I disconnected the sender, but only went to half tank when the feed wire was grounded. Unfortunately it then went to beyond full when I took the wire off the ground, and didn't return. I suspect there is something amiss in the gauge. The pleasures of 50s technology! No getting the laptop out and reblowing the software.

1956 Plus 4 4 seater