ATC I also fly an auld heap which not only do we turn the master switch off but we also pull the CB isolating the battery bus.
Was in one European airport on a charter and after putting it away for the night and walking out wondered why all the aircraft on the stands had there NAV lights on with nobody in them.
Phone off and hotel found.
Next day when phone got turned on 20-30 missed calls telling me to go back and turn the NAV lights on because local safety procedures state that aircraft on stand need to have there NAV lights turned on all the time. They got right stroppy about it even when pointed out that it would mean that a diesel GPU would have had to be running all night as we were DC ground power. And night regulations stated that it could only be run for 10mins for start. Bit of a catch22.
ATR's are the same I believe with live circuits even when master switch off and GPU plugged in and live.
Seems a bit daft to be honest to me but can understand with these big fancy machines keeping power on may speed up bring them on line from a cold condition.