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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53016
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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1985 300D: alarm goes..the horn to disconnect it and as I..easy way

Resolved Question:

I have a 1985 300D whose alarm goes off sporatically and for no apparent reason:   I can't seem to find the horn to disconnect it and as I understand it, it may be more complicated than that.

How can I either ensure that it goes off when appropriate, or preferrably, is there an easy way to disconnect it? Thanks. Ger
Submitted: 7 years ago.
Category: Mercedes
Expert:  Marty replied 7 years ago.

Hi Lazzman, is this a 123 chassis Mercedes? You mentioned a 300SD in your other post.



Customer: replied 7 years ago.
Yes, I have two cars, ; a 123 300D and a 140 300SD. The alarm question is for the 300D
Expert:  Marty replied 7 years ago.

Ok, it was rare to see factory installed alarm systems on a 123 chassis. The alarm module on that car should be located under the driver's side dash. I've attached a diagram from the parts catalog, it's #592 in the picture. I would expect the module to be made by Becker, there should be some labels on it. You should be able to simply disconnect the module. Let me know what you find.





Customer: replied 7 years ago.
thanks; is this module easy to find or hidden? I have seen diagrams like this before and it is still next to impossible to find it; also, I have heard that it is hard to just disable as it not only rings the horn, but disables the ignition; is that true?
Expert:  Marty replied 7 years ago.
I can tell you that on all of the other early model Mercedes you can just disconnect the module without issue. I can't imagine that they did anything different on the 123 cars. The information I have says the module is located "Instrument Panel Under LH Side". They didn't really try to hide them on the other cars. If you set the alarm off and disconnect the horn you can probably here the module clicking. The alarm horn is supposed to be under the battery. Mercedes alarm systems were activated with the key in the door lock cylinder. If you have a transmitter you don't have factory alarm.
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