92 Jetta horn keeps blowing with key on

Could be a stuck (or shorted) horn button in the steering wheel.

remove the steering wheel and check the 3 screws which hold the switch down.

Had this problem in my 92 gl. Turns out the wire running though steering column had its insulation rubbed off. Would only stick intermittently and always at the most inconvienient time. New wire pulled through fixxed it

Most likely yes it's a chafed wire in the steering wheel. The horn is actually always powered when the ignition is on and the horn button just completes ground. In your case the wire is already grounding itself.

Thanks to all for the replies. Finally got at it today. There are 2 horns on this car and the one under the front fender was keeping the circuit grounded. Disconnected this one and all OK. This was after I had the steering column and fuse panel dismantled. Might help someone else.

Later

Jimmy