You're talking about the "consumer switched off" circuit which supplies power to things like power seats and mirrors for a limited time after the key is removed. I have no idea if the stock stereo uses this. I'd have to look at the wiring diagram.
My aftermarket stereo uses an adapter to plug into the stock harness connector and it shuts off when the key is removed (switched power through fuse E1).
I'll check the diagram.
Threaded Mode
