Instrument Panel Light Problem - Help Please

[Chris Foust <jchrisf@bright.net>]

I have a 1989 Audi 100 along with a 1988 model 80.  The 100 is having a
problem with the instrument panel lights.  When the headlights are turned
on, there are no panel lights except for the digital clock, and the climate
control temperature light goes out

I thought that I had a bad rheostat. I removed and cleaned it with tuner
cleaner.  After reinstalling it and the panel back into the dash, everything
worked fine for about a day, then the same problem.  I wonder if I have a
cracked circuit board that loses connection when warm.  I say this because
sometimes in the morning, it works.

Does anyone have any suggestions short of buying a new instrument panel?