Horn not working after steering wheel change (not the fuse or horn itself)

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Active Member
Oct 1, 2020
I am stunned and not sure what the heck is going on.

I received a carbon steering wheel and I had to move the internals from the stock to the carbon. All went smoothly - less than a dozen screws - all done.

Strangely however the horn stopped working. Now I know the fuse or horn itself is not an issue because

  • Horn sounds when locking car
  • During testing I once forgot to re-attach the earth cable that caused a constant horn sound

I made sure all springs are in their respective positions etc. and I cannot for the life of me figure out what else it can be.

The car is booked in in Feb for another issue and I intend to ask Mercedes to have a look - does anyone know if they even touch a steering wheel that is modified even though the internals are the same ? Or will I have to move it all back to original before taking to Merc ?
As the steering wheel is non stock, I would expect that MB say they cannot help as they have no data on the steering wheel.

You need to be aware MB techs are not techs, they follow instructions on WIS, there are few knowledgeable mechanics there.
Sounds like some issue with the wiring of the aftermarket wheel. Where did you get it?
It’s not an aftermarket wheel. It’s original OEM where the leather was taken off and carbon added to it. Someone told me it is about the contacts of the airbag to the plate and it needs to adjusted. No clue how or what though
To make a horn sound ie when you push the button it connects up through the earth wire To for it to sound it must be through the earth wire your working the other way about
Yea I noticed. I do wonder if one of the contacts is broken. The plate got four. Three only ‘click’.
Thanks. I am sure the wiring is ok as if I don’t connect the earth the horn sounds continuously. What I need to figure out is how the switching works.

I wonder if the four screws on the airbag pushing down on the rubber feet that are inside the wheel as switching mechanism.
Sounds like it is a push to break switch if the horn sounds with the earth disconnected. The contacts must be stuck closed. Any chance of a picture of the wheel without the air bag in place?
The 'something else' is what I am struggling with - I just don't know how the 'switch' works .. I can see earth but not the 'other end'.
Any metal touching the metal parts of the steering wheel will act as an earth and join up the circuit . That told you once you pulled the earth wire it sounded the horn thats because it going to earth through the screws like pressing the horn push .
Yea no that is clear .. what I mean is - how the mechanism itself works - where it closes the circuit to open or close or whatever the earth connection. On that picture you can see four gold pins - those connect with the screws from the airbag -


Once the airbag is pushed in (I tried outside the wheel) the airbag is essentially flush with said plate. Under the plate you got three springs under those three wide screws. The way the screws are designed, you can tighten them with Thors ... errm .. wrench ... but they still leave play so the plate (then with airbag) can travel inwards) - which I presume closes / opens the earth circuit.

So there doesn't seem too much 'to it' really. The one thing I noticed is - when you screw the plate in, it only travels in three corners, the forth seems locked - almost to a point where you can imagine a screw being too tight. You cannot put any washers down or something so I am not sure if that is even the issues ...

Very frustrating ...

Wished I had access to WIS lol
It is so hard to tell you things when i cant see the steering wheel . They all work with the same idea . the earth fires of the horn .And as i said before if horn operates its going to earth . Only thing i can say to you is refit the old steering wheel and see how that performs .
I got the latest WIS but it’s a nightmare to find what I need lol.
Well would your steering wheel have a air bag ? A part from that it you should not play about with it ,,,might cost you yiour life if it wont work in a smash
Make sure you disconnect the battery when playing with the AirBag. The fault is between the Horn mechanism and the Slip ring connections that come through one of the gaps in the wheel.

On mine, I have 4 wires that covers the Horn, and other 8 wheel controls with the addition of the AirBag Wire
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Oh yea I always disconnect battery and never touch any connectors on airbag. They scare me lol. I even leave the car for ten minutes after disconnecting (I think it even mentions that on the WIS). Anyway. Fixed the horn. These three screws got springs and I noticed that once tightened, bottom left of the bracket does not have any room to move. So loosened bottom screw a bit and now it works. Makes no sense really as I struggled to get those screws loose to begin with, they were so tight. Anyway, time to get a washer and some screw tight and then another attempt to move it around :)


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