Alarm went off - no reason
 

I was just sitting here not 5 minutes ago surfing the net and I heard the alarm go off in my 1986 420SEL, which is parked in the locked garage. The car had been driven last about 3 hours ago, parked in my garage and left. I had not turned the alarm on, in fact I had not even turned the key in the door when I parked it. Just turned the ignition off and came inside. I had to try turn the key several times before it would stop and then when I opened the door it came on again. I opened the hood and tried to find which fuse worked it. I pulled #7 for the horn, but then it came on again, horn and all. I don' t know what made it stop, but it is off now - replaced the fuse and closed the hood. Any ideas as to the cause? I would like to put an end to this as my wife often drives the car and she only has the valet key which will not disarm the alarm. I don't want this happening to her.

The 86 models had bad motion sensing that caused what you described, and were fixed by MB. The fix was to disconnect it. On the 300E the sensor is a "can" under the rear seat, left side. If this was already "fixed", you will have to look further. Ed

Ed,

Can you offer any advice on my '91 SDL? Alarm intermittently activates without any movement, etc.

Was told there was a tow sensor on 1987s ... mine has a device (box with wiring and a long aluminum rod) on the left trunk wheelwell. Is this the sensor or should I look elsewhere?

Thanks.

George, sorry I can not be of help on the '91. My expertise is limited to my experience with the '86.
The motion sensor and tow sensor are the same thing. I was told it was modified or removed in '87. I have seen nothing of what you describe on my '94 wagon. A dealer or other mech, or others on this site will be of more assistance, good luck. Ed

You can always go under the passenger floormat pull up the panel that is under there and diconnect the alarm brain it says becker and there are 2 plugs side by side lenghtways to disconnect.

There's a rubber plug in the driver's door (near the latch) that allows access to the alarm wires to the door handle/lock. Pop that open and see if anything is disconnected.

Please check your personal mail Ed
 

Greetings Ed,

If you could please check your personal mail, I'd appreciate it. I am having problems with my alarm going off on my '86 300E after it's been set up for five to ten minutes. Sometimes it goes off, and other times it doesn't. There has got to be something amiss that is driving the wife nuts.

Thanks,

Charles

Like Ed said,
 

Go under the rear seat, locate a big can looking container and disconnect the wires leading to it. That should take car of it. Sometimes you may have problem with the locks, so it this happens with locking and/or unlocking the car you may need a new lock.
Good luck either way!:p

Hello Can-do
If you sent me a note direct, it did not come through. If you are having a problem with the motion/tow sensor, it should have been "fixed" by MB. Otherwise take a look and if it is not disconnected, then perform the miracle MB "fix" on your own. If it has been "fixed", then you need professional help. good luck, Ed

Unplugged motion sensor
 

Greetings Ed,

I sent you a personal message from this site. You'd have to push the PM button beneath your response to see what the message is. I pulled the back seat out and found the motion sensor on the left side and unplugged it. Hopefully this will fix the problem. Did Mercedes replace the sensor with a different unit as a fix or did they simply unplug it as I did? If they did replace it, how would a person know if the one that is installed is the new and improved part?

Thanks,

Charles

Hi Charles, finally found your message. I learned something new. My '86 started doing the same thing when it was less than a year old. The factory fix was to disconnect it. There was never a replacement or modification. Please note that this disables only the motion/tow feature and does not affect the rest of the alarm, (you might test it to be sure).
I do not know if the later models have a motion/tow sensor incorporated in the alarm system or not.
Hope this clarifies it, regards, Ed
By the way, the way to check it is to roll down the drivers window then lock the car, reach in and open the door from inside and/or pop the hood. The alarm should sound. E

I checked it after the can disconnect
 

Greetings Ed,

I left the hood propped after the disconnect, and tested the system to see if the rest of it worked afterwards. It did, so I guess the test will come when the wife drives it to work and doesn't have to go running back out there ten minutes afterwards to disarm the car.

Thanks,

Charles