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jpboost

Member Since: 13 Apr 2021
Location: Gatwick
Posts: 377

2014 Defender 110 Puma 2.2 SW Keswick Green

Horn stuck on - wiring fault?

Morning all,

at 3am this morning, the horn on my Defender started blaring! and wouldn't stop.

of course my first thoughts were that someone was trying to steal it, so I moved it, blocked it in and eventually had to simply disconnect the battery to be able to stop it waking up the whole village.

In the fresh (rather tired) light of day, I don't think it was an attempted theft. There's no damage anywhere, nothing disconnected or cut, and when I connected the battery, it was quiet.

But on a short local run, The horn started sounding constantly again, and the only thing I could do to stop it was remove a fuse. although the fuse with the 'horn' symbol (F10) didn't do it, I had to remove one (of the several) labelled as the alarm (F20).

I understand that the horn on these have a permanent live feed, and that the various items (switch, 10AS etc) all earth the horn to make it work.

So I'm working on the assumption I've either got a wiring, or possibly Alarm unit (10AS?) fault. The column switch doesn't seem to be faulty.

Has anyone got any helpful experience or tips to share before I go digging around the engine bay in my lunch hour?

13th Apr 2023 10:17am

discomog

Member Since: 09 May 2015
Location: Notts/Lincs Border
Posts: 2527

2015 Defender 90 Puma 2.2 XS CSW Santorini Black

I had exactly the same problem, woken up in the middle of the night with the horn blaring out and had to pull the fuse to stop it. The vehicle was under warranty at the time so took it to my local dealer. They said one of the horns was faulty and replaced it. Sorry cannot tell you what the exact cause was. Defender 90XS SW
Mini Countryman Cooper S
Morgan Plus 8

13th Apr 2023 10:37am

jpboost

Member Since: 13 Apr 2021
Location: Gatwick
Posts: 377

thanks for the additional information.

Nice to know that the horn itself can simply fail in this way. If that's the outcome I'll be quite happy. I'd far rather replace the horn than have to get into wiring tracing and repairs!

13th Apr 2023 10:40am

macfrank

Member Since: 05 Nov 2015
Location: somewhere in the north
Posts: 1080

2015 Defender 110 Puma 2.2 SW Keswick Green

F10 is the fuse to the horn switch on the stalk.
F20 is in parallel to the switch, coming from the alarm relay.
So if F10 did nothing but F20 silenced it, it can't be a fault in the horn itself, sorry.

Also these are switched positive feeds. The horns are connected to permanent ground.
The relay coil is "earthed" by the alarm ECU, triggering the relay, but the relay then connects a positve feed to the horns, so does the horn switch.

So the fault is somewhere along the path ECU to relay (ground), or the relay itself, or from relay to horns via F20 (positive). The latter is less likely because a short to ground here would result in an olfactory sensation, not an audible one

13th Apr 2023 8:29pm

jpboost

Member Since: 13 Apr 2021
Location: Gatwick
Posts: 377

Thanks for that really helpful explanation.

I didn't get much time to look at it yesterday, so I just unplugged the horn and put the fuse back in. At least I didn't get woken up in the middle of the night again.

So, I think I'll probably replace the relay first, then go wire tracing if i still have problems!

Can anyone confirm the location of the horn relay on a 2014 (2015MY) 110?
I've found lots of fuse/relay layout diagrams, but can't locate it.

Cheers

14th Apr 2023 7:59am

macfrank

Member Since: 05 Nov 2015
Location: somewhere in the north
Posts: 1080

It's the brown one, lower row in the fuse box under the steering wheel. Part no AMR1088, I think.

14th Apr 2023 2:07pm

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