AHA! same problem. Did you get it fixed yet? I found the answer to my problems on a random google search. Apparently the cold or something constricts everything in the steering wheel and causes it to push on the horn. Yeah. Don't like the neighbors screaming at me cuz my horn is blaring randomly. I unhooked both horns, but apparently this still drains power with the car off. So. this may be different for you...
I have a 95 lesabre. In the maxifuse relay center under the hood. There are 2 separate covers. under the left cover the second from the left gray relay is for the horn. Can pull that out and clip the black wire, mine had 2 orange 1 green and one black wire I believe. Either that or you can just disconnect the relay from the little hub it plugs into. But If you clip that wire, you can put a push button switch in that ground wire and run it into the car somewhere so you can still use your horn! I have yet to do the switch wiring but I hear it works great. I never realized how much I missed my horn until it was gone