At some point, while at an RVPark or campground in the middle of the night or while you were sightseeing, a covert tactical response team of commandos disabled it!
It used to be that motorhome air-horn owners would very arrogantly and proudly toot their horns, (and occasionally wear a captain's hat), as they rolled out of their site at 4:30 a.m. to hit the road!
Then, sometime in the mid 90s' it became an embarrassment to use the horn, as more people were very likely to give you the one finger salute, and/or throw bacon drippings and rotting vegetables out of your camera's view, (and call the management and/or local police to complain), as you rolled out.
If you do manage to get it working, please never use it within a mile/kilometer of an RVPark or campground, ever. The commandos are ever vigilant.