I did not see any easy way to autoswich video output from a screen to a tv jack, so i came up with one. First you need radio shack part number 274-246 or equivalent. then use this diagram.
The way this works is that when a cable is not plugged in, the video comes into the jack and then right out to the screen. When the jack is inserted, it disconnects and send video out through the cable
You need either a mono 1/8 to phono cable or a stereo 1/8 to phono cable. if you use the stereo cable, you need to use the white jack to get the connection