The emergency start switch is on the left side of the drivers seat base. While seated, reach your left hand down, or get out and examine the seat base from outside and you will see it. It is used if the coach battery is too low to start the engine. By connecting the house battery the engine can be started from it.
If the house battery is too low, you would simply start the engine to charge it. With the engine running you would be able to start the generator to take over charging. Of course if you have shore power, no need for any of that.
2012 Forest River Sunseeker 2300 Chevy