There seems to be an option in the GTX 330 settings that keeps to unit from powering on when receiveing power from the power system.
I flew in two different airplanes and one immediately powered on the transponder, the other one keeps the transponder turned off, until I press ON.
Looking thru the Pilot's Guide and Installation Manual didn't give me any clue.
Can someone help? Seems like an undocumented feature.