1991 Mazda Protege horn sounds in cold weather

My Mazdas horn goes off spontaneously in cold weather in the middle of the night. I had a mechanic try to fix it last winter, and it still seemed a little sensitive if my arm grazed the horn, but at least it wasn't going off at night and I could leave the fuse in. This winter it's back. How can my boyfriend safely remove the horn cover, and is there a simple repair he can do? I have the Haynes manual, but they don't deal with this. Thanks for your guidance.