[Walt Fricke]

Actually, I don't think I have ever measured the voltage where it attaches to the sender. A gauge can be made to work in such a way that the sender wire does not send battery voltage out. One of the tricks in designing these gauges is to make them independent of varying voltage supply, as you might see voltages ranging from 12 to 14+. The gauge might start out with some voltage dividing. Maybe a Wheatstone bridge?

It is not likely that there is a voltage drain between the gauge and your sender,k other than at the sender connection. But you could run a wire externally from the back of the guage to the sender, and see if the gauge behavior changes at all.

Generally, I think that if a guage reads 0 when you ground the sender wire, and infinite when the sender wire is "open," then the sender might be OK and things should work. I tend not to suspect problems with the guages. A jumpy guage, if the wiring is in good shape, is most likely due to a sender which is wearing out.