Try running a seperate ground to the sending unit from a good ground than you can ground out the sending unit mount and if it still doesn't work you can try grounding out the sending unit post,where the wire from the gauge is on, if the gauge is still not working it could be the gauge,or the wire from the gauge to the sending unit if it works when you ground out the sending unit than you'll know it's the ground . also check the ohms on the sender I got one from a hot rod shop and installed it and it did not work so I checked it with my ohm meter and it truned out to be the wrong ohm,10-75 ohm, the box it came in was right but the unit was the wrong one
Pete
