[W126 Coupe] Horns not working

[Gerry Van Zandt]

Hi Ernie,

There is absolutely no correlation between the "light warning" warning lamp on the dash and the horns not working.  And as far as I know, there's no relay/cube in or near the fuse box that controls the horns -- only the 8-ampere fuse #7 for the horn itself (I believe Series 1 W126/C126 cars used fuse #14, a 25-amp fuse).

It's HIGHLY unlikely that both horns themselves would fail simultaneously, indicating that it's probably an electrical issue.  First, replace the fuse in the fuse box, as a matter of course. 

Next, get a helper and check to see (using a multimeter) whether you have power at the horn connections or not.  If you don't have power flowing when you activate the horns (car must be running or in ACC mode with the key turned), then there's an electrical interruption somewhere.  Test at the wire connections at each horn.

You should next off, physically/visually check the wires leading to the horns to make sure they aren't corroded at the connections, or the insulation isn't worn off.  Should be a pretty easy visual inspection.  Perhaps unbolt the horns to check all around them and examine them thoroughly.

This would most likely be at the steering wheel, which is the most obvious (moving) point of failure. Most likely, the circuit is not making contact at the round slip rings.  You will probably need to remove the steering wheel (separate process, and be SURE to disconnect the airbag system under the passenger foot panel and disconnect the battery before pulling the steering wheel, if you have airbag(s)) and clean/check/lubricate the slip rings with special dilectric grease that is intended for connections of this type.

It is also a possibility (though not probable) that the horn switch in the steering wheel itself is bad.  This is a single point of electrical failure, like the slip rings, that would cause both horns not to work.

Lastly, and this is probably a bit of a long shot and ONLY applicable if you have a Series 2 (1986-1991 model year) W126/C126, is that if you have the "dual" horn option for 2-tone/fanfare horns (the exclamation point switch right beneath the ashtray), that may be interrupting the circuit somehow by being shorted somehow.  However, this is an "either/or" switch so it should in one position or the other work.  In any case, it's unlikely that this switch would be an issue (they don't get much use) but again it is in the circuit and thus could be a point of failure that would affect all of the horns.

My best guess, 80%, is the steering wheel contact rings being dirty/corroded/not making contact.  Next would be the steering wheel horn switch, and lastly would be the dual-horn switch if you have such.  Again the fuse is the first thing to check.

If you have a later car, here is the diagram of the horn circuit with all components included:

http://dl.dropbox.com/u/10675111/horns.jpg

Good luck!

Cheers,
Gerry






On Jan 28, 2011, at 11:15 AM, mbcoupes-request at mbcoupes.com wrote:


> 

> My horns stopped working. At the same time, I have a warning light on my dash that an electrical device (light bulb,etc) is malfunctioning.  I checked my fuse and it appears to be in good shape.  I suspect that there is a horn relay somewhere in the circuit but I don't have a wiring diagram; can anyone tell me what and where I should be looking for?

> 

> Thanks,

> Ernie