greg63,
I'm not 100% clear on the workings of your gauge, but I think it is important that the gauge has a proper ground in the dash assembly. This could affect how the gauge compares the 'in dash ground' with the ground provided by the sending unit.
With the way the gauge is constructed, it is usually a work or no-work kind of deal. Your gauge is working, but incorrectly.
If the accuracy of the gauge depends on the variable ground supplied by the sending unit, there could be a possibility that the wire leading to the sender has been damaged and is 'leaking' to its own ground.
These are just guesses on my part though. :confused:
Stuart
