It should be fairly simple to do what you are saying. What you need to do is have two line going into the p-control on your head unit (or system if you have amps).

The idea is that all your stereo components have constant power and switched power (p-control). Your stereo gets turned on when the p-control wire gets power. That is what your ignition does. When in, or beyond the accesory position a 12v charge is sent down the p-control wire which turns on the head unit and amps if you have them. Without this power the system will not know when to turn on.

You really only need a positive and a ground connection to turn on your head unit. Connect the positive and ground connections to the deck but take a second lead off of the positive line, send it through a switch and then connect it to the p-control. When you turn the switch to the on position a 12v signal will be sent through the p-control line telling the head unit to turn on.

So, I see two ways of doing it. One where the stereo is only controlled by the switch and one where the stereo is controlled by the switch and/or the key.

To set it up to be controlled just by the switch use the simple circuit I talked about above. Split the positive line. Send on to the positive on the head unit and one to the switch, then from the switch go to the p-control. When the switch is on, so is the radio. When the switch is off, the radio is off.

The second method, and the one I would suggest is a little more complicated but will allow you to not have to use the switch if the car is on.

It is really a combination of the normal connection and the connection above. Positive split into to lines, one to positive on head unit, one to switch. Swith to p-control. Also connect the normal accesory line to the p-control. This way, if you turn on the car the stereo will work. If you turn off your car the stereo will turn off. If your car is off and you flip the switch, the stereo will turn on. If you turn on the car with the switch on the car will blow up! Just kidding, nothing will happen, the stereo will keep playing.

Just make sure you don't kill your battery :-)

Feel free to email me if that was too confusing, I can draw you a picture or something.

That's a damned good idea. Actually I'd prefer to have a switch that turned off the ding-your-key-is-in-the-ignition-switch-and-the-door-is-open-idiot ding. Or maybe I should just figure out which wire it is and disable it.

Don't forget a fuse up towards the battery

No problem feed as many power supplies into it as you want. They will not fight each other since all will be at zero, if off, or equal battery volts.

Not sure about the power on light though. if power is coming in fro mthe radio the bulb may light with switch off but engine on? may need a diuode downstream of the bulb to stop that. I would try it and see.

Bill D.