flickering battery and parking brake indicator display
 

Both the battery and the parking brake indicator lights on my 92 525ia M50 flickers or stay on intermittantly at the same time while sitting at long stop lights at night with the head lights on, when this happens I noticed the dash lights and head lights dims. The indicator lights would go off as soon as the car gets going. This have not occured during the day. Alternator is a 140 amp Valeo, it has been tested OK by a rebuilter. I've cleaned the ICV, the throttle body, changed the belts and belt tensioners. The indicator lights still flickers at night.

Anyone have any ideas what might be the cause?

Thanks,
glen-sj