There was a discussion a few weeks ago on this forum regarding External Power and how you didn't need the battery switch ON to keep External Power hooked up (not so on the Classic). What isn't clear is whether you can also apply External Power without having the main battery selected ON???If you can't, I'm having trouble understanding the Boeing Wiring Schematics (I suspect a diode has been missed from a diagram). For the Avionics guys... and those with easy access to real Dead Ships.... Wiring Schematic Diagram 24-41-11 shows that the solenoid of the external power contactor can get power from the section of wiring between the external power socket and the External Power contactor contacts A1, B1, C1 (The diagram shows power from this section going through a 3 phase CB "EXT PWR BPCU" to the BPCU, through a Transformer Rectifier and back out of the BPCU (pin 1 of D10898A) to pin 1 of the Ext Power Contactor and on to the solenoid, energising the contactor if the Ground Power Switch is switched on (and the external power source has been deemed to be OK).Gobbledegook to most, but hopefully some whiz out there can help me.Thanks.Cheers.Ian.

Problem solved! I nice gentleman at the PPRuNe site provided an answer....http://www.pprune.org/forums/showthread.ph...276#post1014276Cheers.Ian.