Guages not working on 79 van.

The Temp guage on the above GMC van was not working, it was practically pinned on the hot side. I went to the auto wrecker and grabbed a cluster out of a late 80s model, and bought a brand new
sending unit. Replaced both, no difference. I'll also mention that the gas guage and oil pressure guage are pinned as well. Not worried about those as there are aftermarket fuel (propane) and oil pressure guages that work fine.
Anyway, what would cause the temp guage to read so high? I noticed that as the engine warmed up, the guage would show even higher, so it is having some change, but way out of wack.
Ryan.
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Look, I havent worked on this phase of auto electronics much at all, but I think you are looking at a basic problem in the instrumentation circuitry.
Since you have more than one gauge acting up, I would check wiring for shorts, broken wires, bad grounds, and - if it applies to this GM product - the instrument volage regulator.
The instrument voltage regulator normally provides 5.0 volts DC to the gauges. If that goes out or shorts, or is intermittent, a variety of symptoms is possible.
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