I had that problem. People here helped me. Check the fuse for the horn. (don't just look if it's ok. use a tester, they sometimes look ok, when they're not.)
Then once it's working keep an eye out on it. On my car I have a short somewhere, as I have smoke coming up through the steering wheel. (still haven't hunted it down from where exactly it comes from.
) Hope I can find it soon. I miss driving the Fiero.