This will be very basic information for many, but I've seen this wiring question raised often enough that I thought this that I posted on another site might be helpful:

902.613.511.91, 901.613.623.01, 901.613.504.01 and other Porsche part numbers are simple on-off switches with four terminals labeled 1, 2, 3 and K. When turned off all four terminals are electrically isolated, when turned on, terminals 1, 2 and 3 are connected together. To use only the on-off function hook one (+) input wire to 1, another(+) output wire to 2 and have at it. Most people would like the pilot lamp to work as well. so a jumper wire should be installed from 3 to the center post on the lamp. Since a lamp will not light without a ground, these switches provide an internal electrical connection between K and the lamp housing. Connect K to ground (-) and the lamp will light when the switch is activated. Switches don't care which way the electrons flow, so if you have connected 1, 2 and 3 to the (-) side of a circuit, connect K to the (+) side and the lamp will light just as well.