long standing issue with my horn not working, I have traced it to the steering column shaft not being earthed so hence when hitting the horn button the earth cant be passed back and hence no horn. If I use a piece of wire connected to earth and touch it on the shaft the horn then works as it should. Weird!
Had a bit of time to have a good look and the shaft looses the earth after the fibre coupling at the bottom of the shaft near the pedals. I guess the rivets that go through have corroded hence the issue. Best alternative I can see is to somehow attach a wire that links across this coupling - heath robinson here I come!