This may help
In short, unless you are going to be tapping some power from the magneto for something else just cap the white wire off and forget it.
As mentioned above all you need to do is short the Blue Hot wire and the Black Ground wire with a momentary button to kill the motor.
The regular kits with the plastic throttle mounts have no polarity on the button wires so which wire goes where doesn't matter, BUT on the nice Grubee GT1 and GT2 bikes with the metal throttle mounting bracket the bike ground is actually tied to the black kill button wire so you have to match them or your motor wires or it will never start.
The whole ignition system wiring sucks so I replace it all and add my keyswitch kit to everything I build.
It not only makes a slight performance improvement, it cleans everything up nice and adds a little security.