My 300E factory alarm was working fine till 2 days ago when I parked it in a restaurant and it didnt make the usual sound when it arms. Later that night when I got home I checked it and its not arming. I locked all the doors with the windows down and open door and nothing happens....usually it will activate the alarm. I chcked all the visible fuses in the engine conpartment and their all ok.....any suggestions?

What usual sound does it make when it arms?

Do you have an aftermarket alarm, if so, the main unit may have wigged out since your Mercedes should not make an arming sound when locked.

I can tell you that it is better that it not arm than to have it go off at some in-opertune moment. Like outside a motel at 6 in the morning.

I have never heard my '92 300E make any indication that it armed itself. It has, however, done the aforementioned.

There is a connection between worn tumblers or some other mechanism in the door locks to the alarm system. Have heard of people switching cylinders from Passenger to Driver side. Other than that I am clueless on this problem.

Steve

the horn beeped once. If the alarm was triggered, then the horn would sound and the lights would flicker on and off. I'm 99.9% positive that it's the factory alarm

Aftermarket.

Look under the dash for any wires dangling, you may find them going to some strange concoction of wires and a control unit.

Also look under your rear seat for any signs of aftermarket gadgets.

no its not aftermarket, the unit is in the foot rest ofthe passenger side of the car. I had connected a wire on the back of my radio last week and I didnt think that it had nothing to do with the alarm, but today I removed the cable and the alarm started working fine....part number for the factory alarm is : 126 820 08 26

Someone wired up something to the horn because the OE alarm systems on the w124 and w201 (and others) did not "beep" the horn to alert you that it was armed.

They armed via locking the car from the outside and would go off if the car was opened from the inside (like if someone broke a window and reached in to unlock it).

__________________
Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE

That wire connected to the radio must have been the alarm trigger for radio theft.

I have seen guys install aftermarket systems on cars that already had factory alarms, go figure.

None of the W124s had a factory alarm that flashed the lights and beeped the horn. Is it a keyless entry system?

no its not, only activates with the key in the doors and trunk. But I checked the whole car and could not find an aftermarket alarm...just the original Becker alarm.