Checking the ohms works when you know the ohms you should be seeing., The gauge could be bad, but I'd start with the cheaper route first like connections and the 2 sensors. Swiping something off another ski could narrow it down pretty easily. The gauge should work fine with the compass disconnected, one way to tell if the compass is an issue or not. These gauges aren't cheap, and it's normally the display that goes bad, but there's a fix for that. Also, inside the large connection between the board and lcd screen gets corrosion, may be worth it to take it apart and clean this. I can't remember if the other wires entering the gauge connect to the board via a plug or not, but that could be an problem area. Like I said, may be worth it to open it up before buying another gauge.