Well I think that tells you its nothing to do with the horn button or steering wheel connections - which was the implied cause of the problem by the garage.
Think its time to look at a F2 wiring diagram - find out what controls the horn - eg is there some kind of 'module', whether there is a relay and/or fuse that could have packed a sad and where the wiring runs to check that.
Personally, I'd try and identify if there is a relay and/or fuse involved as that would presumably be the most likely cause of the problem.
If I was after an F1 wiring diagram, I'd turn to the Rave workshop manual. I don't know where such a resource is for the F2. Hopefully others can say.