First thing to do here is to check the guage as it's mounted in the dash: Disconnect the sender wire that goes to the guage at the sender unit. Turn on the key, the guage should read FULL.
Then, ground the sender wire to a good ground, the guage should read EMPTY. If the guage does not read as noted above either the guage is bad or it is not properly grounded to the dash.
If the guage is good, you prolly have a 90 ohm sender in there instead of a 30. You can check the resistance with your ohmmeter.
