Join Date: Jul 2013
Location: Isle of Anglesey, North Wales, UK
Vehicle: SLK 230 Kompressor R170 auto 1997 in Imperial Red
Other Toys: Mostly computers, lots of them, opening a museum one day, maybe.
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Resolved - Help! Horn only works half the time
Days to go before my 1997 R-170 has its umpteenth MOT test, I have a horn problem.
I've spent ages on this, and thought I'd fixed it twice, but it keeps failing, and then working, and then failing with no pattern.
So, the buttons on the steering wheel do work, they do send to the K40 unit.
The K40 looks fine, no bad solder joints. Following instructions from YouTube, yesterday I bypassed the K40 relay with a standard car relay, which clicks when horn pressed, and sends current to horn.
The horn works (though the second one is dead and now unattached). I replaced horn with similar and the same things happens, so not the horn.
So... what happens is, it's working... then I press it and it sort of dies mid blast, then it doesn't work for a while, and then I'll try it again and it's fine. Then it goes again. Arghh. The fact that it makes this funny squonk noise leads me to think it isn't the relay. Or the switches.
One more thing... if I disconnect the horn switch connectors from the K40, all sorts of warning lights come on... which is odd - so even with the new relay connected the K40 is still in the picture... could it be pulling down the horn voltage some how?
Any ideas gratefully received!
Last edited by Avel Du; 05-16-2019 at 09:20 AM.