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Old 02-17-2006, 03:51 PM
Bigpete123's Avatar
Join Date: May 2005
Location: Seattle
Posts: 130
Thumbs up W124 Seat Switch

Hello everyone. My 1990 300ce's seat switches have been acting up for a while now. My girlfriend was in the passenger seat and was really tired, so she decided to recline the seat and sleep while I drove. What a great time for the seat switch to quit working.

I researched the issue and realized that it's very common. I went through lots of threads on how to replace or repair them and found useful bits of info scattered around.

Last night I went ahead and tried to clean the passenger side switch, and it worked beautifully. To "repay" this forum, I thought I'd post my step-by-step instructions. Unfortunately I didn't take pics. On monday, I will be cleaning the driver's side switch, so maybe I'll take pics and add them to this thread later. This project took about 1.5-2hrs cuz I went really slowly. That's only for the passenger side. The driver's side should go much faster since I already know what I'm doing this time. I almost bought new switches, but I saved myself around $250 over buying new switches. I'd say it's worth it!!

My 1990 300ce has the memory buttons (i.e. the green dot and the 1 & 2 buttons) on the driver's side, but no memory on the passenger side. Again, I haven't done the drivers' side yet. I'll post instructions for that if they're significantly different that the passenger side (I doubt they will be though).

Tools/stuff needed: Phillips screw driver, Flat-head screw driver, tweezers (optional, but highly recommended), que-tips, and Electrical Contact cleaner. I bought a spray-bottle for $10 at Radioshack. Click here for an example

1) Remove the plastic buttons from the switch on the door (i.e. the little pieces that are meant to look like the seat bottom, back, and headrest). You might have to pull kind of hard. Some people have said they needed to a screwdriver to pry them off, but mine came off somewhat easily by pulling with my two hands. Don't twist or jiggle them- just pull straight back.

2) Where the button for the "seat back" was, you'll see a thick, hollow plastic peg with a little plastic washer around it. It will be the thickest peg sticking out. Remove that little plastic washer (it will be obvious how to do so when you see it).

3) Pry the plastic trim piece that surrounds the switch off of the door. To my memory, there are about 4 spots where it's clipped onto the door. I started at the top left corner and was able to get it off by only using my hands.

4) Now you'll see 2 phillips screws holding the switch unit in place (one on either side). Unscrew them, being very careful not to drop them inside the door.

5) unplug the relays on the back of the switch unit.

6) Don't try to dissassemble the switch while sitting in your car. Go to a table with good lighting and lay down some white paper towels. There are lots of tiny ball bearings and screws inside the switch and it would suck to lose one of them.

7) Unscrew the single phillips screw on the back of the switch. I recommend holding the unit up in the air with the head of the screw pointing straight down towards the ground. This will require you to point the screwdriver toward the ceiling as you unscrew. I say this because if the unit comes apart, everything will stay inside of it.

8) Lay the unit on the table with on it's back... In other words, set it on the side that the screw was in. Iit should still be in one piece, unless it came apart somehow during step #7. Gently pry the thing apart. You'll see multiple plastic clipping mechanisms all around the switch. Un-do these one at a time and it will start to pop open.

9) BE VERY CAREFUL when you pull the cover off. Again, there are lots of little ball bearings that could spill all over the place and you don't want to lose them.

10) Now you'll see another sign of Mercedes engineering genius. Seriously, I was shocked how detailed this little mechanism was. Take your tweezers and carefully pick up each one of the ball bearings that are either rolling around inside the case, or are properly sitting on the tops of the springs. I put them in a little shot glass while I was working to keep them safe.

11) Spend some time examining how the device works. You'll see that it's very logical and there's a system to it. This way, you'll understand how to put it back together.

12) For each of the "pegs" that are sticking up (i.e. the things that the buttons used to be attached to), there should be a total of 4 ball bearings and two springs. This excludes the "peg" that the headrest button goes on-it's a little different. All of the bearings and springs are identical, so don't worry about mixing them up. Since you've already removed the bearings sitting on the springs, remove each of the springs and put them in a safe place. Just grab them with your tweezers and pull them up out of the holes that they're sitting in.

9) Now if you look down the holes that the springs were in, you'll see another ball bearing in each of them. By now, some of them might have rolled out of their oringinal location (mine were all over the place). No prob, just take them out and put them in a safe place.

10) Gently pull each "peg" out of its location. The ball bearings are gonna roll around. Again, just pick them up and put them somewhere safe. Note that the middle peg (it should have a little white, spring-loaded tip) won't need to come out. Leave it there, cuz it's seated pretty firmly in place. You won't need to remove it to clean the contact points.

11) for each of the pegs that you removed, you'll see some "U-shaped" copper-colord metal pieces. These are the culprits of your seat woes. All of these peices are identical. Take your tweezers and pull them out.

12) On the back side of these U-shaped pieces, there will be little bump things at the ends. These are the parts where the electricity is conducted. You'll probably see that they're gunky (which is a good sign cuz you'll be able to clean them!). Take your que-tips, spray one end with the cleaner, and scrub away at these bump thingies. Clean all of them up.

13) Inside the switch housing, you'll see the corresponding contact points where the things you just cleaned usually sit. Clean those contact points as well, using the que-tips. I don't think that's how you spell que-tips, but you know what I'm talking about.

14) When you're done with all of your cleaning, it's time to reassemble. This is pretty easy. Take each of those metal u-shaped things and reinstall them.

15) Install all of the pegs in their original locations (the ball-bearings and springs will come next). If you're confused about where everything goes, use the front piece of the switch unit to guide you. The holes will make it clear how things are arranged.

16) For each "peg unit" drop a bearing in the hole that the spring goes into. One bearing per hole. Then drop a spring into the holes over the bearings.

17) You should have bearings left over at this point. This is the delicate part. Take carefully set a bearing ontop of each spring. Don't bump the table cuz they'll fall off!

18) GENTLY replace the other half of the switch unit. Again, don't jiggle it around, or those balls will fall off the springs and you'll have to put them back!

19) At this point, if it's all clipped down, you should be able to test it by giving it a little shake. If you hear something rattling around in there, a ball bearing got loose and you need open it back up and repeat step 17.

20) Replace the screw holding the two pieces together. Test all of the switches to make sure that they move correctly.

21) Take it out to the car, plug the relays back in, and see if it worked!! If it did, congrats! Put the unit in the door, put the two screws back on, replace the trim piece, replace the little plastic washer, and snap the buttons back on. And there you have it!! Rejoice in the fact that the stealership didn't take you to the cleaners on a part that just needed a little maintenance!

Let me know if you have any questions!! Good luck.


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Old 02-19-2006, 11:25 PM
Bigpete123's Avatar
Join Date: May 2005
Location: Seattle
Posts: 130
one thing to add

It doesn't look like anybody is interested in this thread, but i need to add one point now that i've done the drivers' side for those who might search for this DIY later.

Before, I alluded to the fact that the two "pegs" for the seat bottom switch are identical. i only said that because I happened to put them in the correct spot when I reassembled them last time. This time I didn't. When you look at them, you'll notice that the plastic housings that the metal dowl/shafts run through extend only on one side. Look at yours and you'll see what i'm talking about. In other words, these pieces aren't symetrical. The "extended" plastic hole needs to be pointed down. If you do this wrong, you'll realize it easily because the switches will only move in one direction rather than two.

good luck!
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Old 02-20-2006, 01:44 AM
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Join Date: Dec 2005
Location: The Bay Area via Phoenix, Chicago and Minnesota.
Posts: 377
Thanks for the effort!

I've done this too on both my 87s, REPEATEDLY! but I'm to a point of diminishing returns as the switchs seems to get "sloppy" the more times it's apart. I've done a bunch of rear door and seat switches, well just about every kind in the car now that I think about it. I even polished all the contacts and bearings to remove oxidation. They seem to last about 3-4 years after an overhaul. Programable are about $122 and nons are $107 through a WorldPac parts jobber.
2016 GLE300d 4-MATIC 38K BROWN!
2012 S350 Bluetec==94k WHITE

2007 ML320 CDI==166K WHITE (FOR SALE)

Under new management:
2005 E320 CDI--140K--WHITE
1995 E300-Diesel-133.5K--THE CAR IS BLUE
1986 300SL--97.5K (European) AND WHITE. Back in Europe!
1991 190E 2.3-73K California Perfect.--WHITE
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Old 02-20-2006, 10:10 AM
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Join Date: Aug 2002
Location: Southeastern PA
Posts: 3,029
Bigpete123, you explained door switch maintanance very clearly ... nice job.
Fred Hoelzle
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Old 02-20-2006, 10:27 AM
Join Date: Apr 2003
Location: NB Canada
Posts: 1,173
Nice write up. You may or may not have reviewed mine, so I'll post the link for info for those who may be unsure of their skills. I took some picures, so these might help interpreting your text too. Power Seat Switch Cleaning

...And, I'm sorry if you're offended in any way, I didn't mean to 'highjack' this thread, but any responses to mine naturally bump it to the top. I thought between the 2, with pics you don't need to take, it would be a benefit.
1986 560SL
2002 Toyota Camry
1993 Lexus

Last edited by donbryce; 02-20-2006 at 05:54 PM.
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Old 02-20-2006, 01:47 PM
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Join Date: Feb 2006
Location: Jasper, TX
Posts: 31
Red face

Nice job of reporting DIY. Next time you do this job, you may want to put a dab of dielectric grease, with a Q-tip, on the contact points after they have been cleaned. This should extend the life of this completed job. Just a thought.

1987 300E
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Old 02-20-2006, 02:19 PM
Bigpete123's Avatar
Join Date: May 2005
Location: Seattle
Posts: 130
yeah, good call. The Radioshack stuff I got is called "Control/Contact Cleaner & Lubricant", but I doubt it actually prevents oxidation.
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Old 02-20-2006, 04:06 PM
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Join Date: Jul 2003
Location: Bellevue WA
Posts: 174
Good write up

I plan to do this project this weekend. Very timely. Thanks.
87 300D 265Kmi
Factory rebuilt crate 603.96x engine at 200K
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Old 06-12-2006, 04:02 PM
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Join Date: Apr 2006
Location: Virginia
Posts: 235
Just about to embark on this, thanks for the writeup Pete
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Old 06-13-2006, 12:08 AM
Bob G's Avatar
Bob G
Join Date: Dec 2002
Location: Long Beach ,California
Posts: 276
Wink seat switch repair

I enjoyed you article on repairing the seat switch. Would you give us some pictures during your disasemblie of the drivers side? I down loadeedd your article. I do better with pictures some how with out them its harder to reference the material you told us.
Thank you for spending the time to share this information with us.

Bob Geco
1987 W124 140.000 miles
1968 280SL
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Old 06-23-2006, 06:48 PM
Bigpete123's Avatar
Join Date: May 2005
Location: Seattle
Posts: 130
Hey man. Sorry it took me so long to reply, I just happened to come accross this thread.

Unfortunately, I did not take any pictures. I didn't actually own a digital camera at the time. Here's my advice for you:

Dive in and go for it. Print out my write-up, and just take it step by step. I agree that it's often difficult to interpret instructions like this without pictures, but once you get into it my instructions will be much more clear. It's a pretty easy job, so there's honestly nothing to be apprehensive about.

If you look at the above replies, you'll see that donbryce posted a link to another thread he started that includes some pictures. So they might help, too.

Good luck!
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Old 10-15-2010, 10:25 AM
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Join Date: Nov 2002
Location: Frankfort, Il.
Posts: 264
seat switch

Easier and more fun to go to the junk yard and pick up new used switches, I have a whole bucket full of seat and window switches that I picked up for free

'05 Ford Escape 100,000 miles
'87 560SL 92000 miles
'89 300TE 199,000 miles
'02 Audi TT 100,000 miles
'00 Ford Excursion V-10 121000 miles
'92 Mercury Capri 100000 miles
'02 BMW 325XI 60000 miles
'92 230CE 160000
'87 BMW 535SI 160,000 miles
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