When the switch is in the STOP position, there is a contact at the back of the switch that grounds-out the ignition coil thereby shutting down the engine.
40:1 according to this site>
http://www.acresinternet.com/cscc.nsf/ed1d619968136da688256af40002b8f7/98ff65f86b956a2188256dee005b7cc3?OpenDocument
Shooter, September 2009