Weird,weird lighting problem!

[Robert W Obrien <rwo@u.arizona.edu>]

Good morning listers,
This is almost inconsequential compared to some of the stuff the Audi Gods
throw at us, I know, but it goes against the grain of all my elctrical
knowledge: Car- 87 5000T. Problem- dash lights do not light. Computer and
AC lights are dimmed with headlights on, but I am flying blind. Weird
twist: This Audi answer to Saab's "black panel" can be defeated. If I
switch on the headlights before starting the motor, the lights work.

Like I said, minute in scope compared to Phil's burning GT, or q
driveshafts gone bad, but *why*?

This started three days ago. I can't remember to turn the lights on first,
and besides, would rather not add the strain to the battery on startup. 

Where to begin?

In the meantime, imagine the dialogue:

Officer:"Did you know how fast you were going?"
Me, on night banzai run, pointing to dash: "weeeell... actually..."

TIA,
Rob

1987 5000 GT Turbo (and thanks for the badge, Christian!)