[ray_mcavoy]

Grounding the sense terminal on the gauge should cause it to read empty (like you're seeing), not full.

For additional testing purposes, connecting the gauge sense terminal to through a 15 Ohm resistor to ground should cause it to read half. Connecting it through a 30 Ohm resistor to ground should cause it to read full. And leaving the sense terminal disconnected should cause the gauge to peg beyond full.