Thanks for all the replies...!
I always wondered why the Dukes of Hazzard were always running away from the police - now I know! Maybe if they'd put a switch under the bonnet, they could have changed the horn to a single tone and they wouldn't have been in so much trouble all the time?! After, the never meant no harm...
Just for the record - the horns I've got are for "show use only." Happy now? And there's no single note facility on them - they are de de der der der de de der der der derrrrr all the way. My motivation for buying them - they were only £35 and I thought it would be rude not to buy them!
So, anyone got a wiring diagram? Pleeeeeeeeeeeeeeeeeease?