Is there a fuse for the gas gauge in a 1966 Valiant

A flooded float will cause the same symptoms and is very common. If the sender is an original one, don't throw it away, as many of the new replacement ones are terribly inaccurate. There are places (at least there used to be) where you can have your original rewound with better resulting accuracy. Sometimes a slight repair and/or adjustment is all it needs.