If you have a simple test probe with a light you can test the power side of the guage and make sure you have power. If you then touch the sending unit side of the guage the guage should move. I know it's difficult to get to while standing on your head under the dash so you can do the same by probing the wires that connect to the guage.
You can also test the fuel sending unit with an ohm meter. It should read between 0 and 30 ohms.
