Figured I'd share this fix.
I have a 1997 Dakota SLT 4x4 with the 5.2L V8 Engine.

So a couple years ago my horn just started going off, on it's own, for no good reason. Of course, the first time was about 3am. My neighbors were thrilled. I disconnected the battery to make it stop.
Took it to the shop and they couldn't fix the problem. Honestly though, I'm not sure how long they spent on it.
I ended up disconnecting the horn, since this isn't a daily driver.

Over labor day, I finally got around to fixing the horn. It was still blaring when I reconnected it.
Swapped the relays, they were fine.
Checked the fuses, they were fine.
Horn is still locked in ON.
Disconnected the air bag, and it stopped. The pressure pad to activate the horn is INSIDE the front cover of the airbag. It's not a part that's easy to source. Went to the pick a part and pulled an airbag cover for $10.
Replaced that and everything works like it's supposed to.