While the car is running, remove the sending wire from the back of the gauge. This will peg the gauge, on one end or the other.
Reconnect the above wire, and then remove the ground wire from the back of the gauge. This will peg the gauge, on one end or the other.
From the above, you will then know if the fault is due to an open on that wire or the other.
Thanks - DM
P.S. - Different strokes for different folks, but I thought that the VDO style that you selected was too "busy", and so I picked a different style for mine (below).
