Irregular horn

[Lee T]

A couple of weeks ago car locked on driveway, the horn suddenly sounds continuously. I unlocked the car but the horn continued, so disconnected the battery and did a Norwegian reset and left it for 30mns. Reconnected the neg lead and no horn Great I think and before I can tighten the nut, off it goes again only this time it's a 5 second beep a pause then continuous.
I have since checked fuse and fuse boxes, all clean dry.
Changed horn for a PPD twin set and replaced loom from horn to multi plug. Changed the bonnet switch, although original is working. Tried changing the horn buttons with a known working pair to no avail. If I pull the fuse from the cabin fuse box then replace it, the horn will sound either immediately or within 2 mns. From info here I believe that the horn relay is a black one on the back of the cabin fuse box and is not a simple pull out like usual. (was that a decision by the same person who chose the clutch master location) Does anyone know if or how this relay can be removed or have an early Diesel cabin fuse box for sale.

Lee.

[Kearton]

Have you checked the condition of the battery? If its voltage is too low it can trigger the alarm & so sound the horn.

[Lee T]

Thanks for your suggestion. It is the main horn that is sounding, the alarm horn is located in the n/s plenum. I noticed a distinctly different sound after fitting the PPD twin horns and replacing the loom from horn to multi plug in the hope of solving the problem.Also with the horn fuse removed, I still get the toot if I lock the car with bonnet open. I need to know how to remove the relay without damaging anything.

[SD1too]

Originally Posted by Lee T

... with the horn fuse removed, I still get the toot if I lock the car with bonnet open.

Hi Lee,

Looking at the wiring diagram, the bonnet switch has nothing to do with the horn.
Also, with the horn fuse removed there will be no supply to both the relay coil and contacts so it cannot sound.

Are you certain that your car has a separate distinctive alarm "sounder" in the plenum? I seem to remember that some trim levels use a horn which can easily be confused with the "service" horn operated by the steering wheel switches.

I would begin by charging your battery as Kearton suggested earlier.

Simon

[Lee T]

Hi Simon,
The bonnet switch was changed as I had a new one and the slam panel was off at the time.
Yes there a 3 horns 2 on the slam panel and 1 under the plenum splash shield. With the fuse removed horn buttons are inoperative and if I lock the car with the bonnet open I can hear the toot coming from the plenum distinctly. Also I have removed the plenum cover and seen the horn many times. My car does not have a BBUS. Have just replaced the battery as suggested, one I removed was 12.5V replacement is 12.8V and within 3 mns of replacing horn fuse, twin horns constantly sounding again. I can only assume it's the relay as everything else on the car is working perfectly. I have a FBH but the BUS wire has been cut as suggested by Trebor and if it's not the relay I'm out of ideas at this point.

Lee.

[SD1too]

Originally Posted by Lee T

... within 3 mns of replacing horn fuse, twin horns constantly sounding again. I can only assume it's the relay ...

Assumptions are best avoided Lee! Relays are normally extremely reliable.

Originally Posted by Lee T

... as everything else on the car is working perfectly.

What about the rotary coupler? In the wiring diagram this carries both legs of the horn switches which makes it worth checking for a short circuit.

If you can unplug connector C0082 (6 pins, white) at the underside of the steering column that should isolate the coupler. Now try again; are the horns still sounding within 3 minutes?

Simon

[Lee T]

Hi Simon,
I have checked every wire and replaced some wiring, along with new horns and I have tried another set of horn buttons. I did consider the coupler but have never heard of one failing and cannot find any posts detailing failures. So I assumed the relay as there was nothing else I could see in the wiring diagram that may cause the scenario I'm experiencing. Replace the horn fuse (cabin fuse box) and horn sounds either immediately or within 3mns. Sometimes a constant sound and other times a short burst or two then constant. I am No expert in electronics but surely a short circuit would not display that random behaviour but my albeit minimal knowledge of relays tells me it could be relay failure. Does rave detail how to remove the horn relay without a tow rope or a slide hammer .

Thanks. Lee.

[SD1too]

Originally Posted by Lee T

... there was nothing else I could see in the wiring diagram that may cause the scenario I'm experiencing.

There are actually two things; an intermittent short circuit in the rotary coupler or a faulty diode which is shown in series with the relay coil to earth.

You said that you've never heard of a rotary coupler failing. Have you heard of a horn relay failing? I haven't.

There is nothing in Rave about the horn relay other than the circuit diagram.

You can test the relay using the method I described in my last post. I am happy to continue helping you with an electrical diagnosis if you want to do that. I wouldn't be at all surprised if dismantling and observation reveals what's happening here and it could well be something that's impossible for either of us to predict.

Simon

[Lee T]

I may be leaning towards relay over the coupler as it's a simpler job, with a normal relay. I will try your suggestion and unplug the coupler. If it's not that it at least narrows the search.
Can't say I remember a horn relay failing but I have replaced failed ones and even reliable relays can and do fail.
I can only find references to a pcb the relay is soldered onto. Explains why I couldn't remove it.
Appreciate any and all suggestions, unplugging the coupler was a good one and I'll post the results asap hopefully with an answer. There's lots of posts of horns not working but not one with my cars symptoms, so yes it will be interesting to find the cause.

Thanks. Lee

[Arctic]

Hi Lee.
double check the multiplug next to the washer bottle for any chaffing or corrosion of it's spades, spray with some contact cleaner, and push in and out a few times making sure that they are locked together correctly.