Mercedes 500SL R129 mirror mind of it's own, bad earth. help

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Active Member
Feb 18, 2018
Porsche 964 + 997, Eunos Roadster Turbo, VR6, Focus RS
If anyone can help with this, I will reward you! This is really frustrating me and I would really like to solve it myself.

Ok, so when I bought the car, the mirrors and steering column didn’t work, a new module, the one which goes in the passenger footwell was replaced with one claimed to be good from eBay. I fitted that and my steering work, the mirrors worked but as soon as I turn the car on, engine running, the passenger mirror constantly tries to move in 1 direction by itself no matter what the switch is set to and the other mirror just don’t work, along with the steering column.

If I turn the car off, open the door, everything works perfectly apart from some of the warning lights gently lighting up on the dash as well as the lights on the roll bar and snow chain button when move the steering wheel button in and up and right, mirror button, down and left.

As soon as I put ignition on,

Passenger mirror goes back into moving by itself mode and nothing else works.

If I turn the car on, still nothing works and the passenger mirror moves faster..

Turn car off, nothing works.

Close door and open again, everything works as it should but the warning light up, initially the ABS/ASR, temp display back light and then the rest fade on. This is all when operating the mirror/steering buttons in the mentioned directions.

I pulled the passenger seat out, removed passenger door card, visually checked wires, all appears good and untouched.

I have swapped the passenger mirror to the drivers side and it operates fine, so I don’t believe the issue to be the mirror itself.

I am at a loss as to what I should do next! At the moment, I have 1 of the 2 plugs going in to the module, this allows my steering column adjuster to work but not the mirrors.


I noticed some sort of distribution block next to this module, it has a wire doing into the wiring for the mirrors, when I unplug this, I lose all power to steering and mirrors, so I think this may be the connection the car. Operating the mirror buttons has no effect on warning lights etc when I unplug the connection here. The plug from the module wiring into the distribution block has 4 wires, 3 pins, a ground and then a black/red wire which looks doubled up and a blue/grey wire

So, that’s where I am. I am about to go out and unplug the mirror switch to see if this stops the mirror moving by itself but I’m not hopeful. I am sure there is a crossed wire/bad earth somewhere but I just don’t know where!! I had removed the passenger seat in order to see the earth point under there but it all looked clean!


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