W129 - Fed up with same old electrical problems


Active Member
Dec 15, 2006
Northern France
W129 300SL

Sorry but I need advice again. Over the weekend, I got my car (1990 W129 300 SL - US Spec) out of her winter hibernation - started first go, gave her a wash/polish, checked out levels and tyre pressure and was looking forward to topless motoring.

BUT on my first run out I suffered two problems that have bugged the hell out of me for the last couple of years ...... I fiddle around trying various things to sort them out but they always seem to come back.

!. The seatbelt warning light on the dash stays on and the associated audible warning (beeper) will not stop. I've tried cleaning contacts and squirting WD40 into seatbelt anchor points but to no avail.

2. The alarm system seems to have a mind of it's own. If I lock the car using the plip or the key the alarm appears to set correctly but when I unlock the car using the plip or the key the alarm does not seem to disarm.
Everything seems to be ok until I start the car - starts ok but alarm goes off and keeps going until I turn off engine, get out of car and use plip to relock the car. Last year, I was told to replace the fuses which did for a short while seem to solve the problem but this was only temporary.

I'd like to disable the seatbelt warning and alarm because I'm fed up with trying to solve the problems - I know, I could take it to the local dealer but they are bandits and would rip me off.

Any suggestions would be welcome.


MB Enthusiast
May 3, 2005
Echo Beach
R129, Leon Cupra 290, BMW R100
Does it coincide with folding the backrest forwards?

I normally get that alert kicking off if I haven't put it back properly, a good slam closed normally solves it.

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