I just upgraded the radio stack from the Cessna radios and audio
panel to a Garmin package (audio panel, 430 and transponder).
I noticed that the instrument panel light (red overhead) is now
on what appears to be near full intensity when in the off position.
When I rotate the control to highest intensity I can see a slight
change (increase) in intensity. The lamp will not extinguish in
any postion. The only change to this circuit was the disconnection
of the radio display intensity circuit. It is my understanding
that the two circuits are separate. The cessna service manual
does not provide a detail of the circuit description so I cannot
verify that this is a true statement. Transistors should not fail
the way these symptoms appear so I assume they are ok.

My suspicion is that the rheostat may be failing. With the dual
rheostat, my fear is the part will be in the multiple hundreds of
dollars. I need to find a small allen wrench to remove the two
knobs and remove the switch for testing. I thought I would ask
for suggestions before removing and testing the control.

Does anyone know if these circuits can affect each other?
Have you seen this problem before?
Any suggentions will be appreciated.

I don't believe that the problem was caused by the service done
to the ac. I cannot verify that the problem did not exit before
the upgrade.
Tom