HELLO FELLOWS,
My '87 300 TDT has an aux fan that will not come on. If I unplug the two wire switch (blue) the fan does not come on at high speed. If I hot wire the fan at the fan connection, the fan works good. Why is the high speed not coming on?
I took a test light and noticed that there is less than 12 volts going to the temp sensor on top of engine (blue). Could that be the problem?

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1987 300TDT 165K MILES