'88 5ktq Dash Lights

[Wolff <quattro200@earthlink.net>]

On my "new" '88 5ktq the dash lights are intermittent. The cruise
control display and lights on the abs switch and defroster switch are
also intermittent. They will all go on and off randomly while the car is
idling with the headlights on. Sometimes just the dash lights will go
out, but usually all of them do, then they come back on. The stalk pod
for the light switches was loose, but I have tightened it and still have
the same problem. There is a button on the dash that says "lamp test".
It does nothing. The rotory knob to the left of the lamp test button
also does nothing. This is the dash lamp dimmer right? Any suggestions
of where to start on this problem? Can I pull the "lamp test" assembly
out without removing the entire dash?
TIA,
Wolff
'91 200 tq
'88 5ktq
'87.5 coupe
'86 4kq
'84 4k LTD (just sold it)