Gas gauge reads empty even when tank is full?
Defective in tank sending unit or the float has a hole in it and it's full of gas and stays at the bottom of the tank sending a false reading. Usually it's the latter issue. Floats cost about $8.00 at Napa.
It could also be the fuel pump wiring harness is corroded. It is under the car (exposed to the elements), just behind the driver's seat. My gas gauge has been flaky for a couple of years. Now the fuel pump cuts out occasionally and I have to reach under and wiggle the harness to be able to start the car.