Temp & fuel gauges - what am I overlooking?

If it came with resistors, what are they? Look at the post 3, bottom left, in the yellow. Those are the test resistors for low, 1/2, and full scale. All you do is connect them from the sender terminal of the gauge to ground. you of course must have at least 12.6 (fully charged battery) connected to the cluster and a cluster ground point.

That IS the definitive test, AKA, "end to end." Power to the cluster, all assembled, working IVR, and test resistors. if that does not give correct results, then WITH THAT connected in place, check the input voltage to the IVR by pobing the trace up to the IVR, maybe pull the IVR out a little and probe right on the IVR power terminal directly. Then make sure it is grounded. Same deal. Check voltage at the battery NEG, and voltage at the IVR ground terminal. Should be zero. it is difficult to check the IVR output for accuracy, unless RTE give you destructions. It is difficult to check the gauges, but I bet Redfish has some ideas. If you have a known good gauge, you can "rig" it in series with a questionable one, and use 1 or 2 D cells and the two gauges should rise to the same reading.

https://www.google.com/url?sa=t&sou...h-wKegQIFBAD&usg=AOvVaw1wPCCUIXGVPVpClRryNDGb

https://www.google.com/search?num=1...HVp4EyYQtKgLegQIFRAB&biw=1067&bih=475&dpr=1.5