84 Grand Wagoneer fuel guage.

if your jeep is 1980 or newer, it is is grounding issue to the fuel tank sending unit. you can simply take the ground wire from the sending unit and ground it to the body using one of the sending unit access panel screws, just be sure to sand a small area around the screw to remove any paint or rust to you have a good connection, then paint over the area with a dab of paint or undercoating to prevent rust or corrosion to the connection. the wire usually goes through the loom to a different ground, sometimes right to the frame and the original connection will be corroded or rusty.