The metal spade is what you wire your kill switch to. If the switch is open the engine will run. If the switch is closed. the engine will not run. The other side of the kill switch connects to the metal of the crankcase.

The engine has magneto ignition and does not require a battery to run. It will run on it's own without anything connected to the ignition. If you connect the spade to the engine block electrically, the ignition will not work.

Enjoy,

Jim