This is on a C6 or C5? My C5, the horn sometimes works, sometimes it doesn't. I believe it's due to the angle of the steering wheel, which has nothing to do with your car, but I like to talk about me. Anyway, if it's a C5, any time there are electrical issues, it's either a low battery, which you shouldn't have, or the grounds/electrical connectors are dirty. There's 6 of them on the car that should be cleaned. Clean those and see if your problem goes away. If not, and I have time, I'll see if I can find what the wiring schematic looks like to see if there are any other possible solutions.