Fuse for the horn keeps blowing

[Jonff]

As the title says, the fuse for the horn keeps blowing as soon as I press the horn.

A few months ago it happened, I replaced the fuse and had no problems up until today. Any ideas what might be causing this?

Cheers.

 

[Jonff]

Also what is the AMP rating for the fuse for the horn? The one that was in there originally was a 15, I'm presuming that's the right one as I've been trying 15s and they've just blown straight away.