Here's what I found out after a little testing.

My startup situation is default Cessna with
- battery off
- generator off
- avionics off

Now it seems that this setting is applied to the 727 when I load it. Interestingly, switching the batttery on or off on the flight engineers panel does not really switch the battery on. Even starting the APU and closing the breakers and generators does not turn it on.
You can check this by loading the GPS - it remains dark. In order to light up the avionics/GPS, I had to assign hot keys to all three components - battery, avionics, generator. Only when I use the hotkeys for battery and avionics, the GPS swichtes on. Only then I'm able to start the engines, too.
After starting the engines, I have to use the hot key for turning on the generator - closing all breakers on the engineers panel does not turn on the generators. You can check this with the default GPS too - if you don't use the hot key, it will turn off after a few minutes.

Then I changed the dark& cold settings to :
- battery on
- avionics on
- generator on

With this setting, I'm absolutely not able to start the engines, no matter what settings I use on the engineers panel or which hot keys I use.

Nevertheless, I think the 727 is really a great addon. It is one of only three addons that I use permanently, because the VC, the flight dynamics and the handling is very unique and very well done. I'm very much looking forward to the next service pack, though..

Kind regards,
Juergen