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Finishing up non working items on my ,51 M38. All my gauges were original. Unfortunately I had to replace the temp. gauge. Did all the checks and got positive results by the book until it came to reading the ohms of resistance of the sender. It had resistance and it changed with temp. All three senders I have, including the new one, would not operate my original gauge. It would show full temp grounded, but nothing except come up to zero with the switch on. The new gauge works. So, does this mean the gauge is out of calibration with the sender in ohms? The old gauge had a black plastic extension with a funky resister in it, the new gauge does not. I had all the connections clean and pretty with the old gauge. I also wonder if the senders would work with a 120-240 range temp gauge? Mine are 60-260 originally. Are there different senders for each type 24 volt M series gauges? I may have to ask John B. this question also. Any knowledge with these? John

The original gauge you have is the early left over WWII gauges converted for use in a 24V system. They had a built in a resistor in the extension to reduce the voltage. The sender should have worked with either as long as the gauge was the 260 swing and not the 240 swing. The 240 swing took a different sending unit.
John

Thanks John. The gauge does read full temp. when powered up and grounded. Is it repairable? It's in nice shape, I hate to give up on it. John