Just thought I'd share some experience I just had trying to get my Garmin GPS on a switchable power source in my C5...

The gist of the problem is I wanted my GPS on switched power so that when I start the car the GPS turns on, and when I shut off the car the GPS shuts off. Seems simple right? Well it really didn't seem to be. I started by removing the radio to see if there were any wires I could tap into. There didn't seem to be any, but I later came to find that there is (pin 8 the dark green wire) but it's only hot when the radio is on. This is fine for me as the radio is always on when I'm driving anyways. However the voltage on the dark green wire is only 11.5 volts not 12+ like the power connectors have and this wasn't enough to keep the GPS running without kicking over to the battery...

Sooo in the end what I ended up doing is buying a small relay switch at Radio Shack and using the dark green wire as the switch for the power adaptor (cigarette lighter) power. All of the wires are tucked behind the console so everything is hidden. As an added touch I put a small switch in the cubby hole to switch the GPS from always on power to switched power. That way I can switch over to always on power to let the GPS charge overnight if I need to (this does need to be done occasionally on garmin gps's or the battery will die)

It all works really good now. I'm sure there was an easier way, however I couldn't find any switched power wires other than the cig lighter adaptor that had 12 or more volts... Hope this helps anyone else looking to do the same with an electronic device (radar, viewscreen, etc...)