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Old 06-20-2007, 02:49 PM
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Join Date: Jan 2006
Location: Bellingham, WA
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Auto alarm goes off - AT RANDOM - 126

Help. 1990 300 SE, 85K miles
My factory car alarm has started going off at random. Honk of horn and blinking headlights. It's quite embarrassing. I have to stop, get out, put the key in the door and turn to disengage the alarm. I'll go another mile and it happens again. Yesterday I just opened the driver's door, it was unlocked, and it went off. The horn is behind the engine fire wall, I can't get to it to disconnect it, and brother is it loud.
I am guessing the alarm control module is failing. Where is that item and can I unplug it? If I unplug it will the car operate? Should I replace it with the factory unit or get an aftermarket installed?
Does anyone have any other ideas or helpful hints.
Thank you very much.
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  #2  
Old 06-20-2007, 07:00 PM
Larry Delor's Avatar
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Join Date: Jun 1999
Location: Sarasota, Fl.
Posts: 3,112
I had this happen. Somebody on here suggested, that after I unlock the car and open the door, I unlock it again (turn the key a second time, as if unlocking it). This kept the alarm from coming on again. Incidentally, this started to happen, after a big rain storm - I suspect some sort of switch got wet and then corrosion did its thing.

Try that - if it works, great, if not, check back here.
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  #3  
Old 06-20-2007, 07:50 PM
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Join Date: Aug 2003
Location: Wilmington, NC
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Have the same car- had the same problem.

Remove passenger footwell carpeting and there are two multi-prong plugs going into the control box, which is on the left side of the footwell. Think it
says becker on it.

Remove both.

The red plug which looks similar is the airbag connector, which is in the middle of the footwell, so don't disconnect that one (obviously).

You can test to make sure the alarm is disarmed by rolling down a window, locking the doors with the key and then pulling the plunger up- which will sound the alarm when it is working properly.
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'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

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1980 300SD
1992 400E
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Old 06-20-2007, 08:17 PM
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Join Date: Aug 2006
Location: San Diego, California
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look under the rear passenger seat first and see if the anti tow sensor is connected, if it is unplug it, those things are known to cause this issue, so much so that the dealer would often disconnect it due to false alarms. it is a round white container looking unit, on the rear passenger side. if that doesn't stop the activation then disconnect the control unit as mentioned above.
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