What ended up being your problem I have got this same problem now . I haven’t seen any reply please shareJim, the very same thing just happened to me! I have a 2007 Z06 and have always washed under the hood without any problems on late model cars. I washed the engine compartment, sprayed it out and finished the entire car. I went inside and about an hour later the horn is stuck on and I race to the garage and try hitting all the alarm buttons on the keyfob but that just made it crazier! I started the car and ran it for 2-3 minutes and the horns stopped. Back to my den for a beer and about 20 minutes later the horns started up again but this time, instead of one long blaring horn, it now is beeping a horn the way you might say "hello!" or you go first! then it turned into the beeping a really pissed off driver would do! " I store the car at my office when its not home, so thinking I had better get this car out of my neigborhood, and maybe a fast hit drive would dry out the relay panel or whatever it was that got soaked enough to misfire
The 15 minute drive to the office was filled with a lot of puzzled looks from other drivers wonderd what was the problem with the guy in the Vette!
It seemed to beep less......I will wait and see what it is waiting for me when I'm back in the office tomorrow!