First thing to try is run a ground wire from the sender metal tube at the tank to the frame.
See if the guage moves. Originally there should be a ground strap on the sender that straddles the short rubber tube from sender to the long metal tube run on the frame. The ground wire will substitute for it if it is missing.
If still nothing...
Be sure your tank is under 1/2 tank, the lower the better.
Buy a proper sender wrench and pull the one you have.
There is a how to for repairing the sender.
If it does not look like the one in the how to it may have replaced before.
It might be a later model A body but might be repaiable.
Once it is out, you can check it for resistance change when you move the arm, also check the float for being filled with fuel.
