Pin (12) becomes grounded when the switch is on.
Pin (11) activates the defogger relay.
Pin (13) gets +12V from the relay when the switch is on.The light turns on when there is 12V across (13) and (12). -Cut the wire going to (13) -The part of wire (13) going into the defogger switch (the one with the connector ) should connect to the wire that activates the water pump. This should be the green wire coming out of the Snow Performance boost pressure module. This is also the same green wire that connects to the red wire on the actual Snow Performance water pump. This will turn on the defogger switch light when the water pump turns on. -The other part of wire (13), the one that goes to the relay, should connect to the +12V wire that powers the whole WI system. This is the red wire on the Snow Performance boost pressure module. I looked at this image from the online 300zx service manual:
and I also compared it to a 95 and 95 service manual that I have. They all appear to function the same way. I haven't done this myself and I'm basing my findings on the diagrams. One way you can check is by disconnecting pin (13) and checking the voltage when the switch is on and off. The voltage should be +12V when the switch is on and 0V when the switch is off. Also, when the switch is on and pin (13) is disconnected the light should not turn on. 
*********************************
 |
