1999 Buick LeSabre - the horn goes off by itself. Sometimes for a few seconds and other times it blows until I go and press the center of the horn, then it stops.

SOURCE: 1999 buick leSabre manual trunk release

disconnecting the battery may reset it

SOURCE: 1995 Buick LeSabre - horn blows

My horn would honk without any assistance from me. The reason was because the plastic cover for the air bag and horn switches had shrunk so tight that it pressed on the horn switches. If your problem is intermittent then cold temperature would also cause the cover to shrink. This is how I solved the problem on my 1995 Buick LeSabre:
Disconnect the negative battery cable.

1. Under the hood I found a long black plastic cover with the words, “Maxi-Fuse/Relay Center”

2. 2. There are two plastic twist locks (turn ¼ left) and one small wing nut holding the cover on. When the cover is off I see two black fuse covers side by side and below them are several relays. Some are gray and some are black.
3. My horn relay was the second from the left as I faced the rear of my car. It was gray. Some may be black.
4. A small green retainer tab had to be pushed out before I could pull the relay out. On the back of the relay were two orange wires that supply 12V. One green wire that goes to the horns and one black wire for ground that goes to the horn switch under the air bag.
5. I cut the black wire and wired in a spst push button switch that I connected to ground.
6. I mounted the push button switch near the driver’s door on a flat part of the dash. I used very strong double sided tape to secure the button switch to the dash.

My horns now are activated when I push my new horn switch button. My problem solved.

Someone recommended removing the air bag/horn switch unit from the steering wheel and relieving the tightness of the plastic cover. There are probably more than one way to this.

SOURCE: 1995 Buick Lesabre horn blows continiously.

One simple solution would be to act european and use your bright lights to let folks know you are miffed instead of the horn. j/k

I agree that it is something internal to the airbag module. Looking at the steering wheel you see a vertical line running down the center where you would press for the horn. Under the covering are thin pieces of plastic that have circuits in them. Most of it is within the plastic, but in a few places they bare. They are seperated by a very tiny gap. Then you push on the covering you close the gap against the hard plastic layer that actually covers the airbag. This closes the circuit and turns the horn on. Normally when you release pressure they seperate again and the horn stops / turns off. It sounds like somehow the thin sheets have become stuck together and the horn is now always on. I cannot think of a good way to fix the stuck problem short of replacing the airbag module.

SOURCE: 1992 buick lesabre horn wont work are there fuses and where

on a removable panel under the steeering column marked fuse panel and some times the are located in the glovebox

SOURCE: my 1999 buick Lesabre will not start even though

It may be the ignition switch key cylinder. My Buick did the same. Everything worked except starting. Dealer replaced cylinder and reprogramed two ignition keys. Copst, $504.