interior light help

Mon May 28 12:43:51 EDT 2001

Hello.
The interior lights on my 1991 90 have stopped working.  The instrument panel gauges, the aux gauges, and the light around the ciggarette lighter all do not work.  Also the trip computer and climate control do not dim when the head lights are turned on like they are supposed to.  Do all of these lights share a common ground or power source?? I have a bently but i'm not very good at reading wiring diagrams.  I have checked all the fuses and none are blown.  
thanks
keith