Dalton, I appreciate your simple test procedures. I am having what I believe to be regulator issues and will use your test to confirm. My question, however is, what leads the regulator to go bad?

In my case I have a 124.133 (87 300D Turbo) and at about the 21 year mark the fan stared to make grinding sounds (over months) and died...figuring it was probably bad, I replaced it to find the fan didn't run "as it should". Would a failed blower motor cause the blower regulator to fail?

Additionally, I have one observation on my installation of my blower motor...I noticed that on hook-up and checking its performance before reassembly of the unit that the motor (with ignition on) runs constantly. Do you have any comments on this with regards to correct functioning of the control unit and regulator?

Mike

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MIKE
1987 300D Turbo, 225K
124.133/603.960