'57, I had a problem with my gas gauge as well. You really need to make sure the place where the gauge contacts the dash is clean in order to ground. Then, temporarily connect a wire from the lead on the gauge that goes to the sending unit and run it directly to the frame somewhere. When this is connected, the gauge should read full. If not, the problem is at this end. If it works, the problem is at the sending unit end or in the wire from sending unit to gauge.
