Ok. Here's a quick way to determine if your gauge isn't functioning or your sender (the part in the fuel tank that tells the gauge what to read) isn't functioning. You may need a partner

1. With power on/key on

2. Find the access plate above the fuel tank that provides access to the fuel sender. The sender will be a 1.5-inch plate with two wires attached. One is power (the center wire) and one is ground (the little tab on the side)

3. "Ground out" the sender by placing a conductive metal --like a screwdriver shaft across the ground tab and the center positive terminal. A small jumper wire with alligator clips makes this easier.

4. With the sender grounded as above, the gauge should pin and read full. If it does, you know the gauge works and the sender is the problem.

5. If it doesn't, then it could be either or both. Start by tracing the wires from the back of the gauge. Fuel gauge power lead is pink colored per ABYC. Look for bad connections, frayed wire, corrosion. Etc. If you have a multimter, check for continuity. If not do a visual inspection for the whole length of the run all the way to the sender.

if that checks out , do the same for the ground lead.

Good Luck
( and keep her topped-off til you fix it!)

Kevin