Today I unplugged the aux.pump and grounded what I believe to be the blower fan temp switch, on the thermostat?. No change. Interesting though that when I unplugged the blower fan temp switch the fan still worked. I assume this switch simply grounds out when hot. Testing it when hot showed no path to ground. I did replace this switch a couple of years ago. Am I misunderstanding how this switch works?

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1983 300D 280,000
1983 300TD 125,000 Killed by oak tree.
1983 240D Sold
1986 Ford F250 Diesel 6.9l 169,000