To answer your question, There are 4 wires going into the switch: Red (hot wire from battery), Black (bike's main power buss), Brown wire (lighting) and a Brown wire with a white stripe (tail light).
When the switch is off, all the wires are disconnected. When the switch is in the on position, the red is connected to the black wire, and the two brown wires connect together. In the park position, the red wire is connected to the taillight circuit in order to leave the light on so (in theory) someone will see you bike when parked at night and won't hit it. All it's really good for is draining your battery...
The easiest way to wire it would be to put you toggle switch between the red and black wire and connect the brown and brown/white wires together.