The bad translation is the reason why I have been re-writing the manual.

I believe that what Behotec wants to say is that one should not put multiple regulators to the RC input of the control unit/ power supply input of the unit. What they call "switch" in that manual is actually voltage regulator.
The controller need to detect a tension coming from the RC gear input as well as from the power supply input to switch ON.
So basically you need to connect the RC gear input with +, - and signal lines from the receiver.
Similarly, you need to use a separate Lipo 2 S battery as the main power supply for the unit ( ECU battery can be used if big enough).

The brakes/ rudder inputs shall only have the minus and signal wires connected.

Be also careful with the brakes output wiring. The label on the controller is a bit misleading. DO NOT connect the + line to the + connector as marked on the label. Just connect the outer wires as per the picture on the user manual.