They do usually have a earth on one switch that goes to the handle bars that you don't see as it's part of the mounting clamp that's why they only have one kill switch wire VM. Three wires total.
I can't advise what wire goes where as there is nothing that tells you the wiring diagram for the switch on eBay as you check the wiring with an ohm meter when you have the switch in your hand ,the red button is usually the kill switch and the grey button is for the starter solenoid
