I am assuming you have an a-body. But even if you don't. If the horn blows when you hit it find the horn and unplug it. After you do that keep hitting the horn and you will hear a clicking noise . Find that relay that is clicking and unplug it. As stated above if you unplug the horn and not the relay . The relay could stay suck on and get hot without you knowing it is stuck if you don't hear the horn. This could possibly lead to a bigger issue. Smoke. And you know where there is smoke there is ????