My '78 300D's warning buzzer for the seatbelt/door/lights/key doesn't work. Searching the forum I can't come up with any answers on how to get it operational. I have two buzzer relays (one spare I grabbed from the P&P) and can't find any information on testing them aside from plugging them in and seeing if they work. Both of the relays do not but I'm assuming that it is not a common occurrence for these relays to go bad since they are used so very little. Maybe I'm mistaken there.

This warning system in the car hasn't worked since I bought it back in August. I'd like to get it working but can't begin to figure out where to start testing. My FSM doesn't have specifics on servicing the buzzer system, only what conditions it will warn against.

Another problem is that the 10 pin plug that goes to this relay happens to be very common in the car. Common enough that it's on the same harness as my cruise control (also not working ) amplifier plug and the two plugs are roughly the same distance from the fork in the harness where it splits. Not to worry, I'm not swapping anything around since my CC amplifier looks fantastic outside and in and I don't want to fry it. (Inspection of the solder points made me happy that all appear solid and none of the caps on the board have bulged or leaked at all.)

So has anyone bothered to restore this not-so-vital but kind of cool system? Your advice on where to start checking and any hidden fuses/relays/ or common culprits of failure is greatly appreciated.

Thanks all.

Phil Forrest

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1972 220D "Trudy," named by a friend.

"The 220D sounds good... I suspect it is the only car that you need a calendar for, rather than a stopwatch, when doing acceleration tests."
Tom Abrahamsson

Also check the seat switch cable connectors under the seat to insure that there is a good connection. If this is open, the buzzer will not function.

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2012 B Class

1981 300D - Now with greazzer

I recently repaired the warning system on my 1984 300CD. In my case it was the "noise maker" inside the control unit. I was able to get the original buzzer device to work some but it was intermittent at best. I bought a used control unit and it is now reliable.

The noise it makes a bit of a wine, which I suppose is sure to get your attention, so be careful what you wish for. A more modern bong type noise would be more pleasant.

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1984 300CD (sold)
1973 220DPK 4 spd (died)
1978 350SL 4 spd gray market
2003 SLK32 AMG
1988 300CE (sold)
1997 E420 (Totaled)
1998 E320 Wagon