The KZ1000P horn has two wires.
From the KZ1000P wiring diagram
www.google.com/search?q=KZ1000P+wiring+d...rc=cqmTiyuH7iMlhM%3A
it seems to me that one of the two wires is a battery positive wire (probably brown in color) that provides constant battery positive voltage to the horn whenever the ignition switch is in the ON position.
The other horn wire goes to a contact inside the horn button switch.
There's another contact inside the horn button switch that ultimately goes to ground.
Pressing the horn button is supposed to connect the two contacts, whereby the horn becomes grounded and supposedly blowing.
Here's what it looks like on the wiring diagram:
If not already done, would assure that both horn wires are securely connected to their respective contacts inside the horn switch.
Would also inspect the 9 wire connector to assure good clean snug connections through the connector (especially the top two plugs to and from the contacts inside the horn switch).
I suspect there's an imperfect connection somewhere along the grounding line between the horn > switch contacts > ultimate ground.
There may also be a bullet connector on a relatively short black/yellow wire from the battery negative post that provides connection to the wire from the horn switch. Would assure that the bullet connector is clean and snug and providing good contact.
Good Fortune!