Cool man!
To answer your question:
The wiring for the switch is like you said: 12v in (I used a key-switched source), and 12v out back to the jack (not to the light). So the three pronged jack on the back gets a 12v source (ign switched) and has a 12v out that comes from the left knob power switch. I then used that output to send the power-up signal to other components in the system like the MP3 player and amps. A separate power source from the dash lighting circuit was used to power the internal light. That way it's lit when the dash is lit.
Here's a little schematic I threw together for you. Hope it helps:
