You're getting a water from a leak onto your fuse box or control box. Similar thing happened with my g/f's 94 Civic. Her wipers would turn on when they felt like it, her car alarm would sound while driving or in the middle of the night (while NOT being armed), and her horn would come on at any given hour of any given day. I pulled fuses and relays with no resolve. I finally took the entire car alarm system out, miles of wires and BAD connections, as well as disconnected the intermediate wiper harness, and replaced the horn relay......which was packed with mud. Yes, mud.
Turns out years of a tiny leak by the windshield, gave water a chance to drip onto the control box and corrode harness connections and sneak into the horn relay, which was not were it was suppose to be, it was tucked upside down and taped to a support rod behind the dash. The alarm harnesses were all green with corrosion and the wires were barley together. Needless to say, it's all been fixed up without the the use of the intermediate wiper function.
Locate the source of the leak or at least find where the water has damaged. Find your horn relay and check that.
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