Does anyone have an idea how the headlight circuit works on my w126? Specifically, what is the path from combo switch, fuse, light monitoring unit, and the headlight itself.
I believe the combo switch is on its way out since I have to pull back on it for the headlights to work. My work around, jumper wire from parking light fuse to low beam fuse has been working for a couple of months but I would like a more permanant fix besides replacing the combo switch.
Any help is appreciated. Thanks.

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1987 300SDL-268k mi

ON a 1987 SDL the lamp switch powers the combi switch, it powers the fuse & from the fuse to the lamp control module & from the LCM to the light assembly.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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Retired Moderator

Those combo switches do fail at the 20 year point..........the contacts get old and the springs wear out.

You'll need to pull the steering wheel to change it.

Thanks for the info. I wanted to make sure the fuse powers the LCM relay and not directly to the lights. I am not too keen on pulling the steering wheel because this car is my daily driver.
I think I will just install a STDP relay at the fuses to tie the low beams to the parking lights and the high beams to the fog lights.

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1987 300SDL-268k mi

It's not all that difficult. You just need an 18" breaker bar and a 2" x 4" for counter torque..........and a friend is valuable for this task.