I have the exact same issue. I would love to hear if this was resolved.

 

It's not an "issue". It's a direct path to ground through the cruise control switches (and they use the same wire as the horn) so quit worrying about it. Those two buttons weren't meant to be pressed together anyway.

 

It is a built in safety feature. If you ever get car jacked and the jacker is making you drive down the freeway while he points a gun at you and says "relax and don't you dare touch that horn button when you pass that cop or I'll shoot you" You can just say "ooookkkkaaayyy, I'll jjjust relax and pput on the ccruise ok?"

 

I didn't immediately think that was an issue, but my cruise control just recently stopped working as well, so I thought that may have something to do with it.

 

I was driving this afternoon and went to set my cruise control, so I pressed cruise on and my horn went off. I thought I might have just hit the horn by accident so I tried it and sure enough every time I press cruise ON my horn goes off, but cruise control will NOT work...

2003 F250 7.3

 

Years ago all the 7.3 PSD E-Series ambulances we had did this also. Just a quirk.