How do I get to the Horn wiring?

My friend is over here from Florida, and his horn isn't working correctly...we have tried to locate and get to the horn to replace it, but cannot find it. Any help would be greatly appreciated. Is there a Horn relay anywhere? I've located the fuse....but I need to know how in the hell to get to that horn..or a way to get to the negative wire of that horn. oh btw its a 99 GT Convertible

Thanks
Chris