Most of the time it is either the ground at tank or a bad sender. First add the wire that Tim described at see what happens. Secondly, the sender is a rheostat and an arm slides on a coil. The mechanical wiper contact wears it out. The sensor can also have float failure and internal/electrical corrosion. Chances are that your sender is on it's last leg.
If you have to drop the tank to add the wire, then replace the sender also.
Your gas gauge will always "kind of work". Be happy with it if it's close.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
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