At 03:02 PM 2/9/2008, Scott Daniel - Shazam wrote...
>Thanks for the reminder on that.  I haven't done it but as soon as I
>read
>about it here, I thought that's the perfect solution, using the key
>buzzer
>signal from the ignition key to allow power to the radio.  ( use it to
>control a relay of course , not actually supply power to the radio ).

You should be able to drive the radio's "acc" lead directly. Every car
radio I've ever dealt with draws it's working power from the battery
lead, and just uses the accessory lead as a signal - not drawing more
than a few mA from it.