- You must specify exactly how many buses your plane has. 930 provided two buses but then did a bunch of cross-tying behind the scenes in case you didn't have enough power sources.
- X-Plane 940 requires that each battery and generator be on exactly one bus.
- X-Plane 940 will not allow systems to be powered by non-existent buses.
- In 930 it has two buses, battery feeds both buses, and each generator feeds one. You could have systems split by bus and they would work unless you lost one generator and the battery.
- 940 defaults this plane to one bus, because on battery power only one bus will be fed.
- This means that in 940 all of your systems will be reset to bus 1.
Here's a work-around: before you update your plane, make sure you have two battery and two generator switches on your panel. Then open in 940. The import will set 2 buses and your systems will be preserved.
Of course, by the next few betas this may all be moot because we may get something less crazy in there.