Heres a flow i read recently and tested this with the NGX and works as it should, really neat. Demonstrates the detail PMDG modelled the systems.

 

BUS TRANS............................OFF

APU........................................Start

Left APU GEN switch................ON

 

APU GEN OFF BUS light is extinguished

#1 and 2 GEN OFF BUS lights extinguished

#1 TRANSFER BUS OFF and #1 SOURCE OFF lights extinguished

#2 TRANSFER BUS OFF, #2 SOURCE OFF lights illuminated

TR1 indicates 23-32 vdc

TR2 and TR3 indicate 0 vdc, 0 amps

 

BUS TRANS..........................AUTO

 

#2 TRANSFER BUS OFF light extinguished

All TR's indicate 28 vdc and positive amps

 

Right APU GEN switch............ON

 

#2 SOURCE OFF light extinguished

just tried it...perfect! great aricraft!!!