2001 GMC C2500 Horn

Before you go through all about work, have you checked the horn to make sure you are getting power?
have you checked under the hood on the left side of the engine compartment the horn relay it should have power all the time, also will have you checked the fuse? there is also a body control module that is located in the center console, removing the airbag is a little tricky but I can assist you, after I know you have properly diagnosed the malfunction, I'll be waiting for a response.