That key in the ignition buzzer in the horn relay is easy to hear in the car from that location. That's the purpose of it; to warn you that you left the key in ignition when you open the door.

So you don't have that relay with all the wires entering it in my photo?

If it has somehow been moved, maybe you can trace the horn wire back to it. See: http://www.thefirstgensite.com/library/electrical/68wir/68wir1.html