Security System Horn - PeachParts Mercedes-Benz Forum

Hawk180 · #1 11-10-2007, 09:13 PM

You guys have been a tremendous help so far. Here is the last little irritation I have and on my 89 190E 2.6 then she will be good to go. The Security system horn does not work. The lights flash OK and all the other things that are connected to the system works as advertised, but the horn wont sound when the alarm is activated. I replaced the horn with a new one, but I am finding out that there is no voltage coming up on the black/yellow wire that feeds the horn. The brown wire is grounded OK as verified by a multimeter, buy no voltage on the hot wire. Is there a relay that powers the horn only? When I look on the wiring diagram, all I see is that the wire is connected to the N26 bus, but no relay. Where is this N26 bus and am I missing something? Oh, BTW, anyone interested in a 83 240D?

crhenkel · #2 11-11-2007, 12:56 PM

If the hot ( non brown ) wire to the alarm horn has no voltage when the alarm is in the activation mode and the headlamps are flashing to indicate the alarm is working, I would say you likey have a bad alarm control unit. It should be located under the floor carpet in the passenger foot well (front). It is the black plastic rectangular box, usually marked Becker. In any case, I believe it has the contacts and relays built in to it, I didnt think there is an external relay for it. A good note is that all the alarm units from most any W201 W124 and maybe others like the W126 cars seem to be the same. I had a bad unit, set off without the proper trigger, and I replaced it with a control unit from a competely different year and model unit and it works fine, fixed the problem.
I will check the wiring diagrams I have and see if it shows a relay.
Good luck

crhenkel · #3 11-11-2007, 01:40 PM

I rechecked my wire diagram for your car...
The 12v pos trigger for the alarm horn comes from the black and yellow wire from pin 1 of the 8 pin connector on the alarm control unit in the passengers footwell. There is no indication of a relay anywhere in the wiring. If there is one it is built in to the alarm unit I would expect. There is nothing in between pin 1 of the alarm control unit and the positive terminal on the alarm horn shown in the diagram in the MB wiring manual. The ground is continuous to the car chasis and the pos 12v input is controlled by the alarm unit and comes from pin 1 of the 8 pole connector. It you want to test it, go to the passenger floor well and pull the 8 pin connector off the alarm unit. Apply 12volts to pin one of the 8 pole connector and the horn should sound if their is no open curcuit in the wiring from the control unit to the alarm. Or you could just use a DMM to test the continuity from the pin one to the alarm horn and the pos terminal to ground.
Good luck.

Hawk180 · #4 11-11-2007, 02:49 PM

Thanks for your help. I will check the continuity of the wire. If it is OK, I will hit the salvage yards and see if I can come up with a servicable unit that I can get for a substantial savings over the $400.00 plus from the parts vendors. Again, thanks

crhenkel · #5 11-11-2007, 02:52 PM

Keep an eye on Ebay, I think there is one there right now for $80 and it comes with the cruise amp and the SRS voltage capacitor and the panel they mount on. They pop up often on ebay and you can use one from a diff model car like a W124. Good luck, they are stupid expensive even at online shops.
Good luck