This is an old topic, but rather than start a new thread...

I have exactly the same problem. When I set things up via the battery, rather than via external power, none of the lights external will stay on. Basically, I do this:

Battery - TO ISOLATED DC BUS
Co-Pilots AC Instruments      - ISOLATED DC BUS
AC INST & FVM CONT - ESSENTIAL AC BUS
GTC Door Switch - OPEN
GTC Main Switch - START
Wait for the GREEN light...
Bleed Air Valve Switch - OPEN
ATM Control Switch - ON
ATM Generator Switch - RESET then move to ATM GENERATORS

I can get internal lights, but the external lights, like NAV, won't come on. If you hold down the 'L' key, they flash on then go off. With the electrics set up as above, I should be able to get NAV lights on, no?

If I go via the external power route, then there is no problem. But I'd like to be able to get things right with the battery too - the manuals do not indicate any problems with this.

Thanks for any help!

Martin