On my 87 300TD, when I turn the headlights on whether or not the car is running, there is a loud whistling, whirring sound under the hood. If I turn the lights off, it stops. When I turn them back on, the sound comes back. Everything works fine. Is it the voltage regulator. Neighbors can probably hear it when the engine isn't running! Any ideas? Thanks.

I guess it could be the alternator, but my GUESS would be a loose belt or something related.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS

If it makes the same sound with the engine off I would guess its the headlight warning signal (warns to turn lights off with key out). Of course it would have to be malfunctioning to come on with the engine running.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I just had the belt and tensioner replaced last week. Only does it with the headlites on. Does it when the car is on or off. Benzmac. could I bring it by to your shop?

I think I know for sure where the noise is coming from. I have the same problem on my 1990 300E. Whirring sound when headlights turned on, whether engine running or not.

I have isolated the problem to being the headlight wiper motor. Neither one of my headlight wipers works. The driver's side is frozen (can't even move it by hand.) The right side appears to have a broken shaft between the motor and the wiper arm. When I turn my lights on, the wiper motor runs constantly, at high speed. That makes the buzzing sound.

What baffles me is that the wiper motor is only supposed to come on with both the headlight switch and the wiper switch on. I have not taken the components apart yet; my plan is to just disconnect the headlight wiper motors and keep the wipers for decoration.

However, if anyone knows why this occurs, (i.e. could my headlight switch be bad,) then I would like to know. Please note also that on the same side as the bad wiper motor, the fog light comes on without me having pulled the headlight knob out to put it on.

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Don Drake

1990 300E 125k Miles
1994 S420 100k Miles

If you have to replace headlight wiper motors, how much are they ballpark?

When I bought the car last week, the windshield washer pumps were disconnected. I reconnected them and drove home. That is what I am hearing. When you turn on the lights, those pumps come on. The reservoir is empty. I will fill and see if they work. Since the previous owner had them disconnected, I think not.