I was thinking of wiring a radio in my Jeep that is powered through a relay connected to the ignition switch. I want the radio to turn on and off with the vehicle. My question though, how would I add a shutdown delay circuit. What I'd like to have it do is leave the radio on for 5 minutes after the ignition has been turned off. Do I just add a capacitor and timer circuit to the relay? Has anyone done something like this before?