R129 500SL Electric probs - seat, steering, mirrors

MarkGolf

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Hi Guys,

I recently picked up my 1991 500SL.

It's great apart from some electrical gremlins.

The passenger seat, exterior mirrors, interior mirror and steering column fail to operate.

Oddly, the passenger side mirror started moving by itself last night, it was stuck trying to move up, so at least I know it is capable of some movement.

The fuse box appears clean and looks like it has been coated with WD40 at some point to resist corrosion. Otherwise, I have not done any further investigation as I do not know where to start!

The steering column would be my favourite item to sort as it is in a horrible position.

Oh and if at all related, I've managed to pop the window fuses a few times now.

I have ordered some copper fuses to replace the ally ones which are on the car in the hope higher quality fuses may be better.

Otherwise, helpppppp

Thanks for reading
 

Craiglxviii

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Door harness as starter for 10...
 
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MarkGolf

MarkGolf

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The buttons on the door for the seat illuminate on the passenger side if that adds any clues.

So you think I should remove the door panels and check the wiring in there or another end of it?
 

LostKiwi

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As per Craig... door harnesses break over time.

There's also a memory control module responsible for all those things part number 1298200926.

The power seat control module lives under the seat squab.
 
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MarkGolf

MarkGolf

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As per Craig... door harnesses break over time.

There's also a memory control module responsible for all those things part number 1298200926.

The power seat control module lives under the seat squab.

Fantastic. I plan on pulling the squab up to check things out under there.

Where is the memo control module located, sounds like a safe bet in getting a new one, keeping fingers crossed and hoping a replacement brings them back to life! I best check the connections on my current one first however..

Thanks so much!
 

LostKiwi

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Thats the one under the seat.
You may also find your part number is different but will almost certainly end in 26
 
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MarkGolf

MarkGolf

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Great, thank you for that, I'll remove the seat and check.

Fingers crossed
 

LostKiwi

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You get to it from the top. There are two screws at the front of the lower seat squab. Undo them and the squab lifts up. Everything is under the squab.
 
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MarkGolf

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Just had a look, it is damp under there but all connections appeared clean and reseated them all.

My unit has this part number
1298200226.

Im going to try and find a wiring diagram to see what each plug/pin is.

What I did see was a load of earth leads (bottom left of pic) which go into a hole which still looks wet, so I’m wondering if the earth needs cleaning but I’m not aware of where the end of those earths are and how I get to the end..

dateposted-public



Cheers
 

LostKiwi

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Wet isn't good. You need to find the source of the dampness. Any moisture will lead to condensation inside the module.

Put the module in a bag with some rice then put the whole lot in the hot water cupboard if you have one. The .rice will draw any moisture out of the module.
You'll still need to dry out the car interior.
 
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MarkGolf

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Thanks LK.

I think it was wet from the split rear window while in previous owners hands..

I lifted both seat squabs, they both have the same control module so I thinking that I should swap them over..

It is the passenger seat which isn't working but does the module on this side specifically play a part in the steering column/mirror control as opposed to the module on the drivers side?

Thanks
Mark
 

LostKiwi

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Don't know the answer to that sorry but swapping them over will show if thats the issue with the passenger side.
As a temporary repair to the rear windows get some clear polytunnel repair tape (Screwfix do some gorilla tape that works well -my temporary repair worked all last summer till the hard top went back on) and put a strip full length down the outside of the window. Only do the outside as the bend will cause problems if you put it on the inside.
 
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MarkGolf

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Thanks again!

I'm due to book the car in to have the rear windows replaced, the roof itself is in good enough shape to salvage, fortunately the car is in a garage and can dry out now.

Just a question on the soft top roof, I've noticed that from within the car, I can see light coming through where the roof meets the bodywork of the car, I can get my hand through from the outside, is this normal on these? At the very rear, it is nice and tight.
 

LostKiwi

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If its the area I think it is there are steel tension cables that run through a sleeve in the roof to keep it taught to the body. These eventually break but are not a massive job to replace.
 
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MarkGolf

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MarkGolf

MarkGolf

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Just to update.

I swapped the module from the drivers seat to the passenger and it worked!! So I now know for sure that I need a repiar/replacement module.

The mirrors/steering still do not work, I have seen some talk of another module which is under the passenger side dash, so I'm going to pull the carpet back and see if I can spot that tonight.

I have opened up the passenger module, I suspect this got wet as there are water marks on it and in it. I noticed 2 tracks on the PCB had broken, so I've soldered in a wire, I'm hoping this fixes the issue.

40919044831_4ffb9a2bcc_c.jpg
 
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MarkGolf

MarkGolf

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My wire by pass on the broken circuits has failed to work, doh!! So looks like I need to get hold of a new module.

The module for the mirrors/steering also has broken tracks, I tried to solder that but no joy!

So 2 new modules for me. :(
 

LostKiwi

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Often if a track has broken it's because something has overloaded the circuit meaning something else in the module has failed.
 

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