'87 300SDL: Doors closed = no power seats

[eltito]

*Fixed* - Scroll to post #13 **Added a write-up w/ photos, post #17.

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Hello all. I just picked up an '87 300SDL. It's in very good shape, but there's a weird issue that's bugging me.

With the doors open, the power seat adjustments (and steering wheel) work fine, as do the memory settings. Ignition can be on or off, doesn't matter - seats still work.

With the doors closed, however...nothing. No seats, no steering wheel. This is with key on or off. Everything else works (stereo, etc.).

Any ideas?

Thanks!

edit: I wanted to mention that I've tried moving around the relays in the fuse box, as well as replacing all of the fuses which have anything to do with power seat adjustments. Also checked the wiring on the door switches (bottom ones - only ones that affect seat function) and they look like they may as well be new.

[latitude500]

I have a 87 300sdl and I have the same issue. I have to open up the front door to get it to work. I’m thinking that a wire is damaged someone in the system but I’m not sure where to start on the issue. Please let me know if you have an issue.

Thanks

[BoiseBenz]

Same-same with mine. ???

[ah-kay]

I have a similar issue but it is the rear power reclining seat. It would work with door open and would not work with door closed.

I fixed the weird problem - a wire inside the door accordion rubber sheathing is broken. It was touching when the door is in one position but not in the other. I think that would be my first place to check. Check for continuity of wires when the door is open/closed.

Good luck.

[eltito]

Originally Posted by ah-kay

I have a similar issue but it is the rear power reclining seat. It would work with door open and would not work with door closed.

I fixed the weird problem - a wire inside the door accordion rubber sheathing is broken. It was touching when the door is in one position but not in the other. I think that would be my first place to check. Check for continuity of wires when the door is open/closed.

Good luck.

The rear seats adjust too? Or was this an option? I haven't found any controls in the back.

[JimFreeh]

Originally Posted by eltito

The rear seats adjust too? Or was this an option? I haven't found any controls in the back.

Standard on the 560SEL, very rare on any other W126.

Rocker switch on the door next to the window switch operated the recline feature.

Jim

[smitherz]

Originally Posted by eltito

Hello all. I just picked up an '87 300SDL. It's in very good shape, but there's a weird issue that's bugging me.

With the doors open, the power seat adjustments (and steering wheel) work fine, as do the memory settings. Ignition can be on or off, doesn't matter - seats still work.

You didn't happen to get that in Fredericksburg, VA did you?

[Phil]

It's pretty common for all these cars to develop broken wires at the door hinge area. The wires can only bend back and forth so many times before they break. The insulation may look fine but the wires can seperate inside it. I have spliced in new sections on almost all the wires in this area of the drivers door on my car.

[BoiseBenz]

Originally Posted by eltito

The rear seats adjust too? Or was this an option? I haven't found any controls in the back.

It was an option only on v126 with REALLY bad mileage.

[brandlj]

My 86 300sdl has power rear seats, very nice option.

[eltito]

Originally Posted by smitherz

You didn't happen to get that in Fredericksburg, VA did you?

No, this came from Menlo Park, CA (near San Francisco).







Also, anyone know what this knob is? In the engine compartment, at the firewall, driver's side.

[brandlj]

That knob controls the idle speed. It is set on number 4, which is the number Mercedes recommends. It is part of what Mercedes calls EDS, Electronic Diesel System.

[eltito]

There were a few other people who mentioned they had the same problem.

I found out there is a diode in the fuse box which controls the "doors closed" lock-out. Pulled it out and it was fried.

I found a replacement (same numbers) at Radio Shack, removed the old one, soldered the new one into the assembly, replaced and voila! Power seats with the doors closed .

I'll add some pics to help you locate this thing after work today.

Thanks all for the responses!

[TnBob]

The diode part number would be nice too.

[eltito]

Originally Posted by TnBob

The diode part number would be nice too.

Sure thing - I was going to do a little write-up, just don't think the boss would appreciate me using company time to work on it :p. I'll get it done in the next few hours.