Horn just went off

This one's pretty easy. Thank you for providing the additional clue. The clock spring is coming apart. That is a wound-up ribbon cable in a plastic housing under the steering wheel. Normally when the break in the circuit is detected by the Air Bag Computer, it shuts the system down and turns on the warning light to let you know. There are a lot of safeguards built in to prevent the air bag from deploying accidentally but in this case when that cable shreds and allows the horn wires to touch something and turn it on, those bare wires could also touch a bare air bag "initiator" wire and cause it to pop in your face unexpectedly. It is common for those ribbon cables to break on the ends causing those circuits to be dead. It is much less common for the cables to unravel and allow wires to touch unless the warning symptoms have been ignored for a long time. I rarely recommend calling a tow truck when I know so many ways to nurse a car to the repair shop, but this is one where I would be very nervous driving it that way. The computer already has the system shut down and will not command the air bag to deploy. The problem is the computer has no control over what happens beyond that break in the cable. At the very least I would remove the horn fuse so that power source can't pop the air bag. If you have cruise control switches on the steering wheel, those also have voltage that could pop the air bag, but very often there is no separate fuse dedicated to just the cruise control that you can remove.