Horn not working

[Lively]

Had the van for service today and told them the horn wasn’t working.  All he could tell me was there is constant power at the horn and when you push the horn the voltage goes up but the horn is still not working. I imagine there shouldn’t be constant power there until you actually push the horn. I have no idea about wiring and will have to take it to an auto electrician but just said I’d ask here in case this makes any sense to anyone. Any help appreciated 
2008 B9 1.6 turbo diesel

[evdama]

Had the van for service today and told them the horn wasn’t working.  All he could tell me was there is constant power at the horn and when you push the horn the voltage goes up but the horn is still not working. I imagine there shouldn’t be constant power there until you actually push the horn. I have no idea about wiring and will have to take it to an auto electrician but just said I’d ask here in case this makes any sense to anyone. Any help appreciated 
2008 B9 1.6 turbo diesel

Theres plenty of content on the subject if you do a forum search.

Mine was sorted with a replacement fuse but if you have to dig deeper theres corrosion/ furring in the fusebox,bad earth from the steering wheel and bad connects on the horn to investigate.