First check to see if everything is connected correctly. See the link below

Disconnect the wire to the sender it should go one way.

Ground it and it should go the other way.

This will tell you if the gauge is even taking a measurement.

Lets say you have #4714 gauge 0 ohms Empty / 90 ohms Full gauge

Basically when the wire to the sender lead is grounded it should be show empty. When the wire is not touching anything, the gauge should show full. If you can get a 40-50 ohm resistor (should be less than a couple $) the gauge should read about 1/2.