Well, well. There was a quite interesing part 2 of this story. I try to tell it here in case someone has use for it.
When the ring was back on the boss, and everything assembled, the horn worked OK for a while. The the problem returned.
This time the problem was a bit more complicated.
Try to follow me here. Look at this picture:
At the back end of the boss (where the slip ring is) there is a piece of shiny cover. Because of the angle of the boss, the slipring have a bit of contact with this cover.
The cover is made of metal. Since the horn is wired so, that it goes off when the slipring make contact with earth, now that rule goes for the whole shiny cover. I did not realise this at first.
After that my thought was that the culprit could be a screw that holds the contact for the slipring. That could make contact with the cover from the back.
That idea was wrong. There was a bit of insulation on the back of the cover to prevent this.
However. On the bottom part of the steering column, there is another metal cover, covered in some black leather stuff. See this picture:
As you can see, the black stuff has come loose a bit in one corner.
Now for the final part. The horn started when this hapened:
Slipring has contact with shiny metal cover - Shiny metal cover makes contact with the lower cover via the exposed corner - Lower cover has contact with steering column from the underside - Horn starts
Quick solution was easy, remove the lower cover.
Long term solution: fix lower cover and insulate the back of the upper shiny cover.
Me happy
