In article ,
"RST Engineering" wrote:
If the OP checks by turning on pitot heat or the landing light I think
you can diagnose this right away.

THat's true. If it is alternator diodes. I was just thinking that the
dimming he was seeing was from not having the engine turned on and running
on battery alone. That was one of the next questions as soon as he finishes
answering what I've already asked him.


That is correct. The problem exists both with the engine running and
not running. Any other load in the electrical system has no impact on
the problem--it is specific to the intercom and the circuit that
controls the avionics backlighting.


JKG