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Getting ready to fire up my COE and there is an issue with the instrument panel gauges. Wired just like the diagrams posted here.
Regardless of polarity. Low resistance= high gauge readings and high resistance =low gauge reading. Completely opposite from normal operation. Fixed resistance =fixed gauge position that also follows the reverse operation.
So Mark, the masses are not rushing to your rescue, and neither am I, because I don't know much. Something is crazy here as you already know., anytime you reverse the polarity with 12v DC most everything goes the other way. Are the gauges installed in a running engine or is this pre-start testing with fancy meters? The sending units determine the "correct" resistance once operating. I would check the battery ground connection and also run a separate temporary ground wire to the gauge panel and see if that helps.
I currently have the instrument panel out of my 1956 F100 to rewire the truck. On the bench, my fuel gauge operated just like your description and the temp gauge was just the opposite. I will open them up and inspect further when I clean and rebuild the instrument panel. For now, I'm happy they still have movement.
You need to determine how the sending units operate, when is there low resistance and when is there high resistance.
From what I understand these old gauges are a simple bi-metal design that bends when heated from electrical current passing through. The mere fact you get movement when testing them is a good indicator they operate. Maybe not accurate, but they operate. I would determine the operation of the sending units before condemning the gauges.
The gauges in our trucks (if stock) do not operate on variable resistance senders. Many, many threads on here about them, here is the short story.
Polarity doesn't matter a bit. The gauges and the senders have heating elements that act on bimetallic arms that move the needles. You can take ohmmeter readings but what you should find is a constant resistance equal to the heater wires' resistance. Zero resistance means the heater wires are burned up.
Aha, the masses have awakened and I thank you all! My good friend ,neighbor, and fix-it wizard , Neighbor Dave responded as follows:This is direct connection to the gauge. instrument panel removed. each gauge isolated and tested with 12.7 volt from a regulated power supply. Fixed resistors to - neg (in place of tank level sensor, engine coolant, and oil pressure) higher the resistance lower the gauge reading.
I have forwarded your responses on to him to see if he has any further comment or testing.
Regards, Mark.
Ben:
In answer to your question, I have the original shop manual plus the color laminated wiring diagram. Thanks again for your response.
Regards, Mark
Hello all:
Going to check the resistance in the heaters and report back. Below zero wind chills tonight, I will wait till tomorrow to trek to the barn through the snow drifts to check.
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