Just went to move my '04 after getting back from three months in Japan. Horn went off as soon as I opened the door. Pulled the horn relay for the moment. Realized while I was driving it that if I press the horn button, the interior lights and door ajar light would come on.

Cursory look over showed no signs of wiring harness damage. It was a little damp inside, so I moved it into the garage to let it dry out a bit. Won't have time to dig deeper into it for a few days.

Wondering if anyone might have any ideas or has heard of this before?

 

‘A little damp inside’ could mean puddles somewhere else. Investigate where the wires run; and of course look for chew marks on wires.