Both the nav computer and the TV module are capable of running the front display. If you have both, then normally the nav computer is the master and runs the screen. However, if the nav computer fails, then the TV module will take over.

My guess is that your MKIII nav computer is dead, and the TV module is running the display. MKIII failures are relatively common, if they are disconnected from power at the wrong time. If the previous owner disconnected the battery, drained the battery, or jump started the car, that can kill a MKIII nav computer.

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2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input