Well, my horn is not an on/off switch. So that's not a real consideration, I think. Pressing it does nothing to the engine. The button is an old stock Italian button next to the light switch (on/off) for the headlights (this also does nothing to kill the engine).
The horn used to blow non-stop when I first got the moped. Then it stopped. I think someone fixed it for me, but I can't remember now. Anyhow, suddendly it started working again lately. I'm not sure about the cold, since it was MUCH colder earlier and no horn blowing. It's also not because my tail light died (that was MUCH earlier). So ... why suddenly? I have no clue.