my gas gauge is acting weird?" on 1991 Pontiac Bonneville

i thought my gauge was stuck all the way past full, now it goes down to full, when car is off, is it registering at all?
and how can i locate the trouble? thanks...

2 answers
You should check out the fuel level sensor in the fuel tank. You will need a repair manual that includes the specifications for the sensor and a meter to measure the signals to and from the sensor.
sometimes when you have a bad grounding wire to the fuel tank or sending unit it will make the guage read full