1- wheel well fire detection system is powered by which transfer bus?
I've seen NG wiring schematics showing Bus 2. As
de facto says, refer to your latest manuals. There may have been a wiring change or a typographical error discovered which caused the difference between your old and new FCOMs.
2- what happens if the ground power is switched on bus while the bus transfer switch is in the Off position? Which buses are energized?
There are a few variables to consider. It depends on what power was on the busses prior to switching the Transfer Switch to OFF. If External Power was on both busses to start with, and the Transfer Switch is put to OFF, the Bus Tie Breakers (BTB's) remain closed and both AC Transfer Busses remain powered.
Note: The Bus Tie Breakers (BTBs) are magnetically latched in their last position. They need power to both open and close them (not like normal relays which relax into a certain position). Left/Right BTB open/close power comes from their respective Generator Control Units (GCUs). The GCUs must be powered to change the state of the BTBs.
Rgds
NSEU