While driving at 35mph on a city street, my horn started a sustained tone-- not beeps, as an anti-theft alarm, but a steady, sustained tone. I drove to a side street, stopped the car, pressed the center console of the steering wheel-- as thought to honk the horn, once again-- and the blowing stopped. Next day, in the heat of the afternoon sun, the car-- parked outside my office window-- started the same steady tone, once again. I went,out, pressed the enter steering wheel console, and the blowing stopped. In several tries, I pressed the horn console, but could not make the horn do anything but beep once with each press of the console.
Apparently, the horn switch is mounted on a thermoplastic housing, which distorts with the sun'* heat. Although I have tried covering the steering wheel with a piece of cardboard when parked in the PM sun, that did not prevent the horn blows.this past afternoon.
At first, I thought of disconnecting the horn fuse, but that might disconnect something else important. I also thought of simply disconnecting the horn wiring, but could not find the horn in the engine bay.
Suggestions? In my four years of ownership, this never has happened before.

Boilerplate: Void where prohibited, perform at your own risk, professional driver on a closed course, use as directed, no purchase necessary, results may vary, blah, blah, etc.

First: It'* not a good idea to drive without a working horn.

This steering wheel design is notorious for this issue. I own two of these. We used to hear about it a lot, but now a lot of those cars have gone on to their next lives and the remaining cars that had the issue have usually had the horn switch disconnected.

Quick bit of advice: If you disconnect the wiring at the horns in the engine bay, the horn button will still trigger the relay which will drain the battery a little faster than usual. If you want to do it anyways, the horns are located in the front fenders, circled in red here:



It would probably be more productive to remove the horn relay.

The actual problem is that the pad over the air bag and horn trigger pad gets old and contracts a little bit and presses the contact pad. The clearance inside that pad is tiny, like 1mm, and the two sides of the pad are separated by little tiny plastic nubs spaced out between the contacts. It doesn't take much to trigger it. I haven't seen a good solution online for this. Some folks are wiring in a separate horn switch into the wires for the bad one.

Thanks, CathedralCub-- excellent answer. And, yes, I am more than willing to take aggressive action with a fixable problem. The permanent horn bypass switch seems the most direct and permanent solution, especially since I cannot risk horn failure in my urban traffic environment.
First, I must locate the wires to disconnect / bypass.for a second, manual switch, to be located anywhere instantly accessible. Once I find the horn circuit wires, I must ensure I do not disconnect another, important device on the same circuit. I have searched for a schematic, and eventually will find mine, but have not yet.
Second, to buy a switch that is both durable (in frequent use and sun exposure) and responsive to a light touch, as for "beeping" a car ahead to be careful / notice me.
Third, to take immediate action now to prevent the horn'* activation in my quiet neighborhood at 3:15 AM or PM. That will require a temporary disconnection where battery drain does not occur. Suggestions?.
Many thanks for your quick response!

I would disconnect the horn relay. This will allow you time (and quiet) to work on the rest of it.

CathedralCub, will relay disconnection preserve the battery charge? I presume not, but wanted to be sure I had not missed anything.

Of course, I meant to ask, will relay disconnection (still) permit any kind of parasitic drain on the battery?
I presume not, but wanted to be sure I had not missed anything.

This will make it so such that nothing on the car knows that the horn switch pad thing is pressed, so yes.

"any kind" from this horn switch issue, not "any kind" from anything else the car or outside forces.

Thanks, Cub

Cub,
Before I did surgery on the horn circuit problem, I used a
black (opaque) plastic garbage bag over the steering
wheel console to shield it from direct sun.

Has worked, so far. The horn problem never occurred
before the date of my first post on this thread.

BG