The key turns the inner, darker white plastic bit that is holding the spring-loaded metal contacts. They make the necessary connections across the contacts set into the black plastic end piece. The black end bit forces the wishbone shaped contact to sit horizontal and make connections, the lip and the cam on the black plastic bit forces the wishbone to pivot down so that it makes no connection when the key is "OFF" or as the key is turned from "P" to "ON"
I think that's how it works, but I'm happy to be corrected.