I ground the black wire on my 1984 300D, the one behind the upper hose and my fan does not come on. When I jumper the two wires going to the temperature switch on the dryer, the aux
fan runs.

The single wire on my 1980 300SD DOES make the aux fan run when grounded.

I hope someone can answer as to whether the black wire connecting to some kind of temp switch on the thermostat housing is indeed to trigger the aux fan to run. If not what is the purpose of this sensor and wire?

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1980 300SD Manganese Brown Metallic Clearcoat 248k
1979 300SD White 148 k
1984 300D Silver project car for daughter
1982 300D wrecked
1980 300SD 310K not running