I assume the white "thin" cable that goes into the round 3-pin connector and continues as three separate wires is from the key lock itself, and is the one that supplies the vacuum unit with either +B or GND for lock/unlock?

What is the other for? That goes into the door locking mechanism itself. Is it a switch that tells the alarm wheter the door is locked or not? (my car has the factory alarm option).

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99 W210 E220 cdi sedan automatic (248.000 km) 210.006