There are two connections to the horn, one is 6v supply, the other is ground
I suggest you eliminate or prove the horn itself...
unplug the horn connections, wire one up direct to battery negative
connect a flying lead to battery positive (dont allow the free end to touch your bike
touch the free end to the other horn contact tab
does it work?
if it does then next prove the wiring
connect the proper negative connection and repeat the flying lead positive wire test
does it work
if yes then the problem is in the supply from the battery, through the horn push to the horn
if no the problem is in the negative return through to chassis and battery negative