Temp. Gauge Issue

The first thing to do is get some resistors and see if the gauges "have a chance" of reading correct. This includes problems with the gauge units, wiring / connection problems, including the PC board, and the IVR unit itself.

The resistances are

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

you don't need exact. Electronics suppliers such as Mouser, Digikey have these. You used to be able to get them at RadShack. I've got some if you cannot find them let me know.

You just put a resistor from the wire to ground, turn the key on for a couple of minutes to let it stabilized, and the gauge should read close to the resistance indicated, IE 23-25 ohms should give you close to 1/2 scale on the gauge.