The inverter cut off switch should be located on the wall behind your batteries. The inverter also has an on/off switch AND a GFIC reset button.
The Keystone Montana RV Owners manual can be downloaded
Battery (one 100Ah Flooded Lead Acid FLA) are installed at the dealership UNLESS you have the solar package. Then I believe you have one Battleborn 100 Ah battery.
I don't know why you would want to add another water pump.
Owners manuals
https://www.keystonerv.com/owners-manuals
Lots of info here.
https://www.keystonerv.com/product/m...y-fifth-wheels