I have just installed this in a vectra c, as I wanted the ability to
play MP3s.

The head unit has the ability to dim its display when the car lights
are turned on.

However, although the illumination wire is connected to the same pin
on the head unit as the oem head unit, the hu display doesn't dim.

I've checked the illumination wire with a multimeter and it appears
to have varying voltage depending on how bright the dash lights are.

Has anyone had success with auto dimming and kenwood head units ?

Is there another wire in the factory fit loom (maybe in the iso C
connector) that is either 0v or 12v depending on whether the lights
are off or on ?

Cheers