It is sometimes possible for the fuse to develop a hairline crack and thus not pass current while it otherwise visually apears to be good. If you know the horn is good and the relay is clicking, try putting in a new fuse anyway to see if it makes a difference.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record