I wanted to post this in case someone else has the same problem. My son's 2007 6 was blowing the fuse that controls the horn, cruise and brake lights. It was very random with each new fuse lasting a few weeks to a month, and we could never pin down any set of circumstances that would make it blow.

I finally took it to the dealer and they found the problem after almost a full day of looking. Apparently, the horn wires pass close to one of the metal pipes from the AC. The hot wire to the horn had a small worn spot in the insulation, just enough to ground out on the metal pipe if it moved a little.

The mechanic said it was easy to spot as long as you knew where to look. Maybe this will help someone else.

 

Hello! The same thing just started happening w/ my 2007 Mazda 6. I have had to replace the horn fuse 3 times now, in the past month & a half. UGH!
I wanted to thank you for your info, as I'm hoping this is the same reason why my fuse keeps blowing.
THANK YOU!!!!!