Welcome aboard.
Odd problem. So before going further, may I ask how you are certain it doesn't happen above 60mph. Also, how you know that pressing the horn button solves it? I don't intend any disrespect, it's just a question that needs to be asked.
May I also ask about your bike. It's a 2002 Road Star Warrior, right? Or is it a normal Road Star. How long have you had it? Do you know if the several recalls were completed by the dealer?
One other thing. If you post clear pictures of your bike, from both sides and front/back, and also two clear pictures of the hardware and wiring under the rider seat, it will help. If you have pictures of what is under the top fuel tank it will help even more. If not, we can ask for them later (although you probably want to post them anyway so others can help you).
Hang in there. This trouble is probably harder to find than fix.
