I was driving my step-dad's Cadillac and it has an interesting feature that made me think of the recent thread about wiring the radio through the ignition switch. Say you're driving along listening to the radio and you stop and park... you turn of the car and pull out the key, and the radio stays on- until you open the door. It shuts off when the interior lights come on, so the trigger is obvious I guess, but how the rest of it is done, I don't know. I have no idea at this point if it's a feature of the particular radio, the car or if it was a trick that the installers rigged up. The radio isn't hot-wired in the normal sense- you have to turn over the key as normal to get it to come on. It has the power antenna and memory wire if that makes any difference.
I will find out if it has anything to do with the car, but I don't know what I can learn about the other two things. I haven't really given it much thought at this point but I'd like to figure it out. Any ideas?

Cya,
Robert