It has been awhile since I have done anything on the water heater itself but if I remember right you have to have that switch on. That one is wired into the water heater going to the element and comes as part of the water heater. You can turn it on and leave it on. The switch in the camper controls the power going to the water heater to control the power to the element. With the switch on the water heater on you can control the electric side with the camper switch. Its a double switch situation, but one is put on the water heater itself by the heater manufacture but the main control switch is put on by Redwood.
Roger & Cheryl Full Time since 2002, RVing since 1975 2008 Chevy 3500 Crew Cab Dually, 2012 RW 36RL
The switch on the outside is for winterizing. When you drain your tank this will not allow you to turn on the water heater by mistake and burn out the heating element. Turn it on when full andyou start your season and turn it off before winterizing.