The isolator, only works with the ignition on and connects the Aux battery with the engine battery so that both can charge ONLY when the engine is running. However, the Aux is always connected to the electric panel. I'd imagine if you're plugged into 120V ac/ city electric there is another separation there that supplies power first to the electric panel, then to an inverter which goes to a charger which goes to the Aux battery (although I haven't gotten that far yet). Anyways, here is the basic diagram of the Aux. battery with an isolator switch, and power to the 12v side of the electric panel or fuse box.
