Greg,

Sorry for the slow response. We have been on the road for the holidays and I wanted to beat the weather and did not take the time for email etc. We are in California right now. The simple explanation is that any difference in ground between where the gauge is grounded and where the sending unit is grounded causes a current flow that looks to the gauge like a change in the sending unit. When I had a poor ground circuit at the dash I would see a slight change in the gauges when the lights were turned on. Also since the whole circuit is fairly low resistance any problems in the wiring will be reflected in the reading. All my problems, except the fuel gauge sending unit, have been coach wiring. For example the ground connection between the coach and generator was to the generator tray. The connection between the tray and engine block was damaged and was causing my problem.

So far all the gauges in our Wanderlodge seem to follow the Teleflex standard. But they have more than one depending on the series. I have the information at home. I will look around the net the next few days or post it when we return home.

I use an old Resistance Decade box I have when checking my gauges. It lets you dial in the desired resistance. Here is an example of one http://www.mcmelectronics.com/product/TENMA-72-7270-/72-7270 but I would not buy one. I have also used a 250 ohm and a 100 ohm rheostat to test the gauges by setting the resistance using a multimeter.