I am assuming the Kawasaki in question is the same as my Hornet (my previous old Kwakkas were). These have the battery wiring terminated in a crimp connector with a hole for screwing onto the battery terminals. I'm also assuming the battery is good. This may be a big assumption, it may have an internal issue where tapping the case makes a connection.
If it was up to me I would disconnect the cables and pull the battery out.
Clean the battery terminals with very fine sandpaper/emery cloth. If they are rounded off file them flat with a fine file so the crimp connector has a flat surface to sit on.
Clean the crimp connectors themselves with the same sandpaper paying close attention to the state of the wiring attached to the terminals themselves. Do the wires need cutting and re-crimping or are they securely crimped/attached?
Re-assemble everything and ensure the screws holding the wiring to the battery terminals are tight. Does the problem still occur? If not, woo!
If it does follow the cabling and check every component/connector and wire sequentially. You might want to check the connections on the starter motor as the next starting point, the problem with bikes is that everything is out in the weather and gets covered in road grime and other crap. Alas road grime and crap don't conduct electricity and generally will promote corrosion...which also doesn't conduct electricity

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Can you borrow a known-good battery? This may be worth trying too.
Good luck with it, electrical problems can be a bitch.
Mick
