Need help with headlight switch?

[skd2k1]

Does anyone know which wire on the wiring harness for the headlight switch controls the interior illumination?

[skd2k1]

bump

[vfr-rich]

The one that comes out of the dimmer rheostat.

[Tassie_328i]

The diagram that i've got show's it as the Grey/Black one.

From the light switch it goes to the dimmer (and other places), after which it turns into a grey/red wire, then goes off to the different switches / cluster etc.

The actual interior lights (dome light/rear lights) are controlled by the body electronics module. The grey/black wire goes off to it aswell as the dimmer.

Are you tapping something into it?