1st post here, hopefully someone can help...
I have a 99F350 Powerstroke, 209k on it. Been a great truck. Today at work I hear a horn honk in the parking lot. Not an intermittent honk but a honk like someone is laying into it and not gonna let up
( My key fob was in a jacket that was hanging, not in my pocket getting squished). As i walked outside to see what was going on I realized it was my truck. Went back in an grabbed my key fob and hit the unlock button to get horn to stop (again, not intermittent but blaring). Finally got to within 30 feet or so and it stopped. Turned around and went back to work. 10-15 minutes later same thing. Grabbed key fob started hitting the lock/unlock buttons and when i got close enough it quit.
Back to my desk....10-15 minutes later again a blaring horn in the parking lot. This time went out and took the damn fuse out.
I called the local dealer and they are stumped. They suggested unhooking the negative battery cable for 20 minutes then hooking it up and allow elec. system to re-set.
I am afraid to put fuse back in becasue I don't want to hear this at 2AM in front of my house!....any ideas?

 

I had the same problem, on my '05, only it only would happen at 2-3AM. Every couple of months, the horn would just start sounding. I would go outside, push the horn pad on the stearing wheel, and it would quit.

A couple of months ago, it happened again, only this time, it wouldn't quit. Pulled the fuse, and took it into the dealer. What they found was that the airbag was starting to unfold, and depressing the horn switch. They replaced the airbag, and all is well.

Thankfully I still had warranty. Good luck with yours.