1963 gas gauge sending unit malfunction

[lcboyer]

If I remove sending unit from tank and move the float, gas gauge indicates full to empty. When I reinstall it, it shows empty even if tank is full. Any suggestions will be appreciated

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[74 Harley]

It sounds like you have a bad ground or a connection that fails when the wires are in position.

 

[59tbirddavid]

Harley is correct, you are missing the ground. Use a length of wire attached to the tank, cleaned to clean metal somewhere on the gas tank, clamp wire with vice grip pliers. Now touch the other end the wire to the negative post of battery. If gauge still does not function, the structure that the float is attached to isn’t making contact with the gas tank when it is secured.