This circuit is a nice upgrade to you vehicle. It allows your music to still play after you turn your vehicle off until you open the door. The switch in the upper left is the vehicle's accessory wire from the key. The momentary switch would be the ground switched wire from your dome light or the door pin circuit. The LED simulates your radio or other accessory power. This circuit can be adapted to retain power to other things like power windows or 12 volt outlets.
