Gas gauge does not work - 1998 Cadillac DeVille

Cathy, 1996 Mercury cougar gas gauge not working. Simplest thing to check first is your fuel gage fuse, make sure all fuses are good. The ground wire could be corroded/damaged, sending unit in tank faulty, fuel level gauge in cluster faulty. All things can be tested by a good Tech.,diagnosed and estimate for repair.
1994 Mercury Cougar gas gauge don work
Ford Gas Gauge Does Not Work Help Blue Springs Ford Parts Blog
Diagnose Fuel Gauge

It may be the sending unit in the tank that needs replacing. Here's how you can check: Turn the key on and disconnect the sender unit at the gas tank. Ground the sender unit's wire with a jumper wire from the truck's harness to ground. Watch the gauge. If the gauge on the dash is good, grounding the sender wire will cause the gauge needle to react and should move to full. This would indicate a new sending unit is required. If the gauge doesn't move when the sender unit is grounded, the gauge is bad and needs replacing. Pull the instrument cluster out to replace the gas gauge. Likely any old ford gas gauge might work-back then, there were not so many production changes.

There are three possibilities. The gauge could be defective. The instrument panel voltage regulator could be bad or not grounded or (most expensive) it might be the sending unit.

sensor might be malfunction of the circuit might be disconnected.

was the gas tank empty or full some times the gauges won't work untill the tank is full or the wire for the gauge was not put on properly

sounds like a fuse

Have the computer checked

sounds like your missing a ground somewhere.

you requirer anew fuel pump assyb the float is stuck

sounds like you have a grounding problem... the gas gauge works off of resistince....if you ground the gas sender wires you should see the gas gauge drop.. if not check to see if it will drop closer to the gauge.