Wouldn't you be looking for resistance not voltage?

Sounds like an earthing issue to me. If it's like mine where the two wires connect to the gauge there is a small insulating ring between the connector and gauge body. Make sure the small "tab" is not touching the back of the gauge.

Mine did something similar (but in reverse) when this happened on mine.

If the temp gauge is ok you can probably rule out the voltage stabiliser (if you have one).


Richard
1976 4/4 4 Seater