Hi The horn on my diesel van does not work when the ignition is turned on, however, when it is turned off, the horn works. I have been told that the problem might be with the BSI unit, but according to the wiring diagram in the Haynes manual, it is not wired through the BSI. Is the diagram wrong, am I mis-reading the diagram, or does the horn somehow require some sort of signal from the BSI? Any help to clarify or repair this fault would be greatly appreciated.

I had the same problem as many people on the internet and I have come here in the hope that someone can cure it in the same way. The problem was that the horn would work when the ignition was off but not work, or sometimes work intermittently, when the ignition was on. When I took off the steering cowl (not the steering wheel -- too scared of the airbag) I saw a wire going from the key barrel to the back of the steering wheel mounting, and a similar one to the wiring loom on the other side. I took these out, blew into them, pushed them well home and voila! fault cured in time for the MOT. If blowing doesn't work, I guess you could try electrical contact cleaner.

I looked on the internet before and found loads of people describing the problem but no-one really describing the cure, hence this reply. I hope this fix will cure your problem if you are having the same issues.