No ground to the sending unit will do the same thing (indicate full). Shorting the center wire to ground should show empty and ruin the terminal end.

Higher the fuel level, higher the resistance from the sending unit. Current travels from the ignition switch through gauge to the sending unit and out to ground.

First part I replaced on my truck was a fuel sending unit. Memphis Equipment has a universal sending unit that works great.

If we knew the correct resistance of the sending unit at the full position, any universal sending unit could be used. (probably 30 or 90 ohms)