Sorry, but the mk4 is working not this way. The unit has permanent power supply, 12V +-, without ignition. But the unit does not forget the last position not because of the permanent power supply.
After you turn off the ignition, a saving procedure is started. The unit saves the actual datas to non-volatile memory. If there are no IBUS traffic, after the saving procedure the unit goes to sleep, at this point the red LED turns off. If you take out the unit from the car, no matter, the unit remains the saved datas even after 1 year, because the datas are in memory.
The broken mk4 you mentioned, has a defect power part inside, if you turn off the ignition, there are no saving procedure, the unit immediately stops. Therefore you have always the same, previously stored position, destination, settings, what was saved in the past, when the unit worked well.
The unit must wake up if:
- ignition is on, or
- ibus traffic detected (eg. door, trunk opening), or
- eject button is pushed

The ibus traffic monitoring part is defective, so if there are no ignition, and eject button is not pushed, the unit stops without saving tha datas.

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Bombolo