Combination Switch Extra Wire?
 

I have a 1993 124.028 sedan. I recently replaced the combination switch because of a malfunctioning wiper. The new combination switch came from peach parts and had all the same markings and multipoint connection except for a small doughnut wire which I didn't connect. When I got everything back together everything functioned as it should except for the horn. I'll try to get a photo of the connection up ASAP. Any help would be greatly appreciated.

Here is the connection in question:

http://i45.photobucket.com/albums/f6...IMG_3845-1.jpg

Here is the old connection without the circular connector sprouting out:

http://i45.photobucket.com/albums/f6...s/IMG_3848.jpg

For speed sensitive wipers, non-USA

Thanks mbdoc! Any ideas as to why the horn would stop functioning? I've rechecked the connections, contacts, and the fuse.

Actually, respectfully, on the S124, it is for the rear wiper circuity. It completes a connection if the multi-switch is in the wiper-on position AND the car is in reverse, i.e. the back-up lights are on. The rear window wiper automatically comes on when the wipers are on and the car is in reverse.

You can tape it over, or remove the plug cover an desoldier the line. Either way, it won't impact your vehicle (unless you have a wagon, in which case you should plug it in).

This weekend I am going to put the old switch back in to see if the horn functions with it.

I would think the horn is unrelated, the wiring for it doesn't run with the combi switch. Have you checked if you may have damaged the wiring in the column while running the new combi wiring?

I can't say for sure, but I didn't tug at any wires and everything went smoothly installing the combi switch, which is why I figured it had something to do with it. The contacts on the wheel and column look good and when I tightened the airbag it seems to be in place. This is my first MB so I'm not sure about hearing a relay click when you hit the horn, but it isn't doing it currently.

Do horn relays go bad frequently?

I had a problem once before with the horn, but that just turned out to be a bad fuse.

The relays certainly can fail, it's worth a check if you have an extra one around or can sub another from the relay panel. Have you checked for voltage all the way to the horns themselves while the horn is active?

Are there carbon brushes as part of the assembly? I think on the 123 they are part of the combi switch. If they're not swapped over or aligned correctly then the horn won't work.

Dead on! I went back in and compared the old switch and the new one. There were two brushes that were on the old switch and not on the new one. I popped them out and installed them in the new switch and the horn now works.

What confused me were the brushes that were for the airbag. I saw 4 brushed and figured they were all combined. I traced those wires looking for a fault and did not realize that there are two extra brushes for the horn on the combination switch. I'm really glad I didn't immediately trash the old combination switch as I would normally do with old parts.

Thanks everyone for your help!

Never throw away old parts.