petrol gauge not working

in between sanding panels down prior to painting i tried to suss out why my petrol gauge is not working....the water temp gauge works no problem....at the sender unit they is 3 wires....with ignition on i get voltage on the 2 live ones and if i earth them nothing happens....i know this points to the gauge itself but i like to be sure first.....any other things i can do before i ditch the gauge etc

My first landy had a duff petrol gauge it turned out to be the sender unit in the tank. Cost about £15 and 15 minutes to fix but i did need to bend the float arm slightly so it gave a true reading. Good luck.

How are you earthing them? One wire should be the gauge one should be the low fuel warning lamp and the other earth.
If you are using the earth wire and its broken nothing will work, try a known good earth.
They are not a live as you would think, the live feed goes through a voltage stabiliser, through the gauge and earths through the sender.
The voltage stabiliser should also feed your temp gauge which you say is working so that looks ok.