if you have lost the key then you will need to either put a new ignition (key) barrel in the ATV or simply take the ignition out and bypass it which means connect the wires permanently but this means the ATV can be started without a key
hot wire it?
Simply pull out the ignition,cut the red wires and pulled them together but don't connect the black one.When you are done with riding pull out all the wires apart.
Leave it be, if you wind up shorting it out, you guys won't be
friends over this . Depending on the quad, they are a little more
advanced these days with their electronics. Especially the higher
end units like Polaris.... Just wait till he gets his key and then
you guys can ride. It's just not worth the damage you can create
by hotwiring it....