Backup camera mod 04-05 anyone know the pinout to make this happen?

Hi guys & gals,
I want to add a backup camera to my 04 prius and maybe something else later.
Now I could use something like this 2 to 1 Channel RCA Video Intelligent Switcher for Car | eBay or this RCA Video Audio AV Switch Switcher Selector 2 In 1 Out for DVD Camera Car U8U8 | eBay the second one has audio which would only come in handy if I could figure out a way to connect that to the stereo. but that would be a later project I could always do a Bluetooth cassette tape and a Bluetooth dongle on the pi.
however here's the thing one of these would switch the screen to input 1 which would be my backup camera which only gets turned on by reversing because it would get power from the backup light. I'd figure I'd splice in a rca cable where the nav outputs the video signal and add an rca connector on the other side of the wire to go to the nav screen. when the camera comes on the nav screen would switch to backup camera. I'd just have to get used to leaving the mfd on nav instead of fuel efficiency for this to work.
does anyone know what two wires coming from the nav dvd under the seat are the wires for the rca video to splice the video to.
I would use a second box later to splice in the raspberry pi signal to watch movies or something while I'm parked or you tube/hulu/netflix if I'm close enough to wifi.
terramir