Does the gauge go to full and stay there no matter what, does it stay at empty or does the gauge point outside of the range of the gauge (Foe example, WAY far past "full" or any other location besides the range from E to F) If it goes to full and stays there, chances are that the sending unit has gone bad. If it goes to empty and stays there, chances are that the float on the sending unit is not floating and has sunk to the bottom, giving you an empty reading. If the needle has gone all whacky, it is probably a stepper motor in the gauge cluster. The stepper motors used on the gauges in those vehicles are known to be problematic. If it is the float or sending unit, the tank has to come off to replace it. If it is the stepper motor AND you have basic soldering iron skills, it is something you can fix in less than an hour.