The red switch is called the element variation switch.
The red switch controls power to the heating elements, and that's about it, so if the unit is plugged in the controller will still be on and the pump will still function regardless of the switch position, if the switch is turned on the heating elements will work, if the switch is off the heating elements won't function.
Simply leave your Element Variation Switch on 'Normal' or 'l' at all times. The Connect Control Box will change between elements as it needs to, instead of you manually controlling this.