I have a '99 Toyota Landcruiser with a haunted horn. Sometimes the horn will sound continuously while I am driving the car and won’t stop until the fuse is pulled. It has also happen while the car is parked, no key in the ignition. I am now hornless. The dealership can’t figure out what is wrong. I don’t believe it is the alarm system. help
I had this happen on one of my cars and my brother had it happen on his car. In both cases it turned out to be the horn switch in the steering wheel. Locate the horn relay and disconnect the line going to the horn button in the steering wheel. If the problem doesn’t occur when you replace the fuse (you won’t have a horn), this is the problem. If the problem does occur, then the problem is probably the horn relay. On most vehicles, when you press the horn button, you complete the circuit to ground in the relay which pulls the contacts closed to sound the horn. If the wire from the relay up to the horn button is making a ground connection, the horn will sound.
yup, and over time the grease in the steering wheel hub can collect dirt and other crud, and get very sticky. That can hold the horn switch closed as well.
While probably not the cause of your problem, I’d like to relate a story of my own. I had a VW Super Beetle that started beeping the horn at odd moments while driving (usually when some big mean-looking guy was driving towards me 
). It appeared to be related to turning the wheel, so I pulled the steering wheel and examined everything closely. No joy. Eventually I looked under the left-front fender where the horn was mounted. The wires were hanging down a bit more than they should, and the tire had chafed through the insulation. A turn at the right speed and direction would press the bare wires the right way to cause the horn to sound. I don’t know why this just didn’t blow a fuse, but taping up the wires (and pulling them up out of the tire’s path) fixed everything.
I’ve also seen (heard) a number of horns go off during very cold weather, as horn switch parts (or something) contracted in the cold. The fix is usually to pull the fuse until the weather warms up. No great loss, as 99% of people don’t use the horn properly anyway (use it to express annoyance or say hello, not to warn of danger).
On the 1950 Chevrolet pick-up truck that I owned years ago, I had a problem with the horn button in the steering wheel. I bought a button that attached to the side of the steering column–ran one wire to the relay and the other to a ground. I disconnected the wire that went through the column. This worked perfectly.
Check the steering wheel for cracks.
My dad had a Buick many years ago that did the same thing. Turned out that the steering wheel expanded / contracted with heat / cold, and sometimes it would trigger the horn.