89 300 SEL Driver Seat Adjustment

The driver's seat in my 89 300 SEL has had inoperative memory and headrest movement for some time. Fuses were OK and cleaning the switches didn't help, so I've lived with it pending time and motivation to tear into it. Now the seat back angle adjustment has decided to quit too, and I can overlook the problem no longer. When the seat back switch is activated in either direction, there is a relay-type click heard under the seat, but no action from the motor.

So I removed the entire seat, checked and cleaned all plug/socket connections, but found nothing obviously wrong. Applied 12 V DC direct to seat back motor, which works fine. Looks to me like the memory module may be the culprit, but I stopped short of drilling out the security screw to open it up. Having places to go and things to do, I buttoned it all back up.

But now the question: should I open the memory black box and try the old "resolder everything" trick, or is there a better next step? If the memory module is bad, is there a recommended rebuilder?

Addendum: Now the seat back will, occasionally, inch forward spontaneously when the engine is started. Still no response to the switch, except for relay-type clicks under seat. Does this sound even more like the memory module?

Suggestions gratefully appreciated!

Frank Peele

I have replaced many of the control modules for the seat in this model. They were known to fail in this way especially if they ever were wet. You should be able to get a control unit from any Mercedes parts supplier. I don’t think an aftermarket one is available, and if one were I wouldn’t recommend it anyway. Benzmac

thanks for the rapid response! I'll be looking for a replacement module

FRANK
IF YOUR CAR HAS POWER SEATS W/MEMORY ON BOTH SIDES THE CONTROL UNITS ARE IDENICAL.
SO YOU COULD SWAP THEM SIDE TO SIDE. ALSO
IN THE MERCEDES CLUB MAGAZINE "STAR" THERE
ARE REBUILT UNITS OFFERED.