[fulltiming]

The merge switch on the dash likely has three positions. In the upper or lower position the two sets of batteries are tied together for assistance in starting or to charge the chassis batteries off the coach batteries charger.

In the center position, the batteries are isolated as they normally would be.

The difference between the upper and lower positions is the source of power for the solenoid. Most manufacturers assume it will be the chassis batteries that need assistance so they power the solenoid off the house batteries. Of course if the house batteries are dead, you can't merge the two sets of batteries together. Newell put in a switch to allow you to merge the batteries regardless of which set of batteries was flat. The solenoid will be powered off the chassis batteries in one position and off the house batteries in the other position.

You should have two larger manual cutoff switches in the rear of the engine compartment that are easy to spot that isolate the batteries.

I originally thought that the Master switch would kill the house 12 volt power, but as I mentioned earlier, it only is a master for the 12 volt lights in the coach.