Tony,
When you turn the key OFF, does the gauge change position. With 12 volts applied and no ground available, the gauge will read FULL. With 12 volts applied and a jumper from the sending unit terminal on the gauge to ground, the gauge should read MTY...if it doesn't do this, the gauge isn't functioning.
If it does do that, then the wire back to the sending unit is open OR the sending unit/tank is not properly grounded. It's this simple. What happens when you bypass the connection at the fuse block and connect the two wire ends directly.
Is there a connector on the back of the gauge that allows it to be connected one way only...keyed!
http://rmcavoy.freeshell.org/diagrams/66cabwire.jpg Stuart
