Guys - RJ was kind enough to send me a driver's seat switch for my 81 300SD. Unfortunately it has one extra wire. A heavy gauge wire, red with white stripe, in the new switch at left of picture. Wire is shown leftmost on the new switch. What could it be for and can I just cap it off? New switch 11 wires; old switch 10 wires. PS - all the other wires and colors match, old and new.

Thanks for your help.

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I installed it few minutes ago and capped off the new wire. The seat raised up and down but does not go forward or back. However there now seems to be power when I try it forward/back; it shivers but does not exactly move. There is zero reaction on the other adjustment which used to move the seatback forward and back.

I still feel like something needs to be done with the red/white stripe wire?

Ideas?

Not being familiar w/the 81 SD...

It's power. Later models were fused from two sources. 85 had a red/white power wire, earlier had two reds. Didn't think they were soldered to the switch, though... My 84 has a connector to it.

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mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)

MY 81 has a single red wire. Assuming the red is the same gauge as the red/white, should I splice the red/white from the switch to the red from the car? There seems to be no power to the upper control; wonder if this could be the problem?

Thanks.

I tried connecting the red/white stripe wire to the red wire. What it did was to cut out the power to the forward/backward function of the seat. And still the upper control which makes the seat back move did not work. So I unhooked the red/white stripe wire.

What year is the new switch from? I believe I have schematics for the seat switches

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82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

I was told that it is from an 81 300SD. The part number is different from the number on mine.

If you take the red/white wire and cut it, then splice the end going to the switch to the red wire it will power the seat back. What you have when finished is a loose red/white wire from the wire bundle (tape it off) that goes from the door to inside the car and both the red and red/white wires on the switch tied together in a "Y". My 82 euro 500SEC seat switch is hard wired and my 85 300SD has a plug.

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85 300 SD ~ 115K
82 500 SEC Euro ??K
78 450SL 164K

Jim - thanks; I will try it.

Success but not without a setback. I spliced the red/white striped wire as JimandSuzy recommended and magically the seatback began to work too. So I put everything back together. The wire splices made a pretty thick bundle but I was able to smush it down some and get the inside of the door back on. It was tight and you could see some inside pressure on the door facing.

Put everything back together, every screw. Popped the seat control buttons on the new switch and immediately they popped back off. Sure enough, Mercedes built this thing with such close tolerance that the extra little push out was too far for the prongs that hold the seat control buttons. So I took everything apart again, unspliced the wires and contemplated.

The door design has a reveal only for the original bundle of wires which is about half an inch in diameter at most; no room for all the splices that I made using male/female wire connectors - in case I need to take it apart again. Wires cannot be rerouted to the left along the reveal for the door latch rod because the seat control switch fits flush on the doorframe and there is no way to get the wires back past the switch; the switch also sits on a plastic shelf which has a slot to feed the original wiring through. Really an elegant design.

Finally looking to the right I decided to make a circle out of the original wiring in a slight reveal and hold it with duct tape; luckily my splices were long enough that this worked. I was not sure that the doorframe cover would go on but luckily it did. The hooks fit into the holes in the metal doorframe and slid down locking the door cover securely. And it all went back together smoothly.

So I have a properly working seat again and seat control buttons - after at least ten years.

Thanks to RJ for the switch and JimandSuzy, JamesDean, and Charlie for the suggestions. Pictures attached.

I really love this SD. Original owner.

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When you have a bunch of wires that need to be spliced, the best thing to do is stagger the splice location. There's two reasons for this: 1) your wire bundle doesn't develop such a large bulge, and 2) less likelihood of two bare wires touching. Glad to see you could make it work. I love my SD too.

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mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)