Yes, this LCD's dimmer thing is completely uncovered in the documents, i've been trying to figure out how it works for a good while now without a clear result, in the odometer LCD description appears that there is a photocell which controlls it's brightness and it dims on headlamps, for the aircon unit the only thing which proves this circuit's existance is the connector's pins description in the workshop manual where at C0792 pin 1 appears "Night lighting/dimming = Input" in the connector view appears RB wire but this pin/circuit is not shown at all in the diagrams, also the clock's LCD illumination works the same, it dims on headlights but only the main lighting feed is shown from fuse F16... a real mess, from all my research i suspect the IDM so if other problems will appear which can be due to the interior fusebox/IDM(cos it used to suffer from water ingress) and you'll change it this issue might be fixed as well... though i'm not 100% certain in this lack of info about it
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