Go over every inch of the wire loom and look for any spot that has worn through or broken. Lightly pull on each wire going into any connections to see if any pull out easily. Also take the starter switch on the handlebar apart and clean up good, look for any bad connections or places where it could be grounding out. It sounds like the ignition is being ground, just like a dirt bike that you push in a kill button to shut it down.
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