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HELP! Defender Horn keeps going off

M

Monty90

In Second Gear
Having just bought the Defender I have always wanted (Defender TD5 03) I was horrified when the horn started sounding for no apparent reason on Saturday. Continuous horn that woiuld only stop when key was in the ignition on position 2 - and started again as soon as key removed.

Was resolved after driving, but then started again in the dead of night and continued despite removing all horn and alarm fuses

Eventually removed battery so now without car

Any ideas on what this might be? Thought maybe battery dying, but don't want to shell out on a new one on the offchance

Any advice / suggestions from you guys (and girls) would be gratefully received as I want my car back, but can't handle being woken up (along with the rest of the street)!

Thanks

Monty
 
Sounds like you have an alarm problem. Do all your door switches operate the internal light? Is light on all the time? Is switch under bonnet ok? Disconect if you are not sure.

If you lock it via the key this should not set motion sensor. Does it still sound??

Try some of these things, and let us know have you got on.

Andy
 
Mine (a 2000 TD5) did precisely the same thing. And it's nothing to do with the alarm.
Somewhere on the car, a live feed has chafed through it's insulation and shorted to earth. This mucks up the BCU (Body Control Unit) which controls light functions, wipers, electric windows if you have them, and stuff like that - including the horn. Another tell tale sign is if the wipers suddenly develop a mind of their own.
The real problem is trying to find where the short is. Mine was traced to the nearside front side light, where the wiring had all melted together. With hindsight, there were a few give aways. The nearside side light fuse kept blowing even though the bulb holders were all good, and both filaments were intact, and the front nearside side light would fail even though the filament subsequently turned out to be good - the current was being lost to earth.
Happy hunting.
 
As Andy says, it's most likely an alarm problem. It's not described as a BCU in a Defender (that's a Disco thing that does much more) but a simpler 10AS alarm ECU that's a green box located behind the instrument panel.

It would help to get it plugged in to read the alarm events. Does yours have an internal motion sensor (pair of small sensors located above the drivers shoulder)? A faulty one of these would set it off I think, check it as Andy suggests. A failed door or bonnet switch would give a mis-alarm signal and not set it.
 
Body Control Unit, Multi Function Unit, Alarm Control Unit, call it what you want, it's getting a duff feed from somewhere other than the usual places.
My guess is the horn goes off the instant the key is turned to "0" or removed, as opposed to there being a slight pause as one would expect with a normal alarm event triggered by a proxy sensor or door switch.
I also suspect the usual method of silencing the alarm using the key fob does nothing.
 
Thanks all for coming back to me

These are both things I will check out over the weekend

To be clear though, it is the horn that is going off not the siren type alarm

And yes when going off the horn does stop immediately on turning key to position 2 and starts immediately after turning back to 0

So again thanks for the advice, I shall report back!
 
Monty90 said:
And yes when going off the horn does stop immediately on turning key to position 2 and starts immediately after turning back to 0
Click to expand...
Almost certainly not an alarm/alarm sensor fault then. If it were, there'd still be the brief period (30 seconds?) where the alarm is in the pre-armed phase. The fact it's triggered by the ignition circuit points to a simple short somewhere - the difficult bit will be finding it. (Mine ended up at £700 for an auto electrician who methodically went through virtually the entire loom checking the voltage at various points)
Are there any fuses that have been repeatedly popping lately? Or other random stuff happening? Wipers? Rear screen wash?
 
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