I powered my drive + play from some spare fuse sockets using radio shack fuse taps plus fuses. Granted my current draw isnt equal to a hi power radio/amp BUT I an assuming the buss side of the power rail will handle most normal loads (with appropriate fusing )
ng8650s post prompted me to edit mine .. my wiring config gives me the same radio on after key off till door opened scene.. I think I selected fuse position 21 by luck, anyway it powers my Drive+Play, radar detector and soon to be installed Sirius receiver.

 

Just finished rewiring, again , my sirius satellite radio (S-50). I had tapped into the brown ignition wire. The only thing I didn't like was that it turned the power off as soon as the key was in the off position.

I like how the factory radio stays on until you open the door. So I went to Pep Boys and bought an add a fuse. After verifying with a test light, I plugged it into the spare fuse #21 (Center console) and a 10 amp fuse. And now I'm officially happy with my Sirius setup.

Now my Satellite radio turns on once the ignition is in the on position and automatically shuts off once the drivers side door is opened and the key is removed Just the way I like it.

I left an additional connector for later on when I hook up my aftermarket head unit.

Ng