Bad sender unit?

Hi folks-

Just installed a new Agco OEM temp gauge on my 1969 180 diesel. The needle was kind of shakey, then went to full hot ( off the scale ) and stayed there, even though the tractor was cold.. Could the problem be a bad sender unit at the thermostat or is it the gauge? Trouble is the old gauge hasn't worked in years.

Thanks for the reply
Was the sending unit wired for 12V+ or 12V-, it makes a difference. An improperly rewired tractor could also be the problem.
With some tractors, you ground the wire to the sender, it should peg the needle- that means the sender is bad. No reaction, replace the gauge.

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