This happened to me too. first test the bulb as others advised. If it's not the bulb in the dash then it's in the sender inside the gastank. You can renew the sender as follows.

Using all possible precautions for an exposed tank of gasoline (including disconnecting the battery before opening the tank), remove the sender from the tank per the Bentley manual. Recover the hole in the tank to limit gas vapors. Take the sender it to a work place AWAY from the gasoline.

Remove the screw from the bottom of the sender. At the top of the sender are about 8 crimps. These must be filed or dremeled out with a cutting bit. Slide off the casing very carefully (there are small wires running close by the casing down the sides.

The low-fuel switch contacts are at the bottom. Clean these with emory. Also lightly and gently clean the slide wires.

Test out with an ohmmeter to verify proper contact.

Luck!

Ron H.