I did this a while ago, it worked great so I thought I should share. (bmwtips.com)
(I've only found this to work on MKI Navigation Systems....couldn't get it to work on II & III
1. Set ignition to Position II (do not start the car)
2. Enter TV mode
3. Enter "Settings"
4. Enter "Contrast"
5. When the green contract bar is visible, push the knob and keep it pressed.
6. Turn ignition off (keep button pressed)
7. Wait 8~10 seconds (timing must be Acurate)
8. Release the knob
9. Turn on ignition again
10. Your TV Video is now working (hopefully) along with your audio.
I've also attached an Aux Video / AV connection...ill post instructions/pictures some time....