Firstly, your picture of the 'Rocker Switch Example' on the right of your drawing is absolutely correct;
The switch has 3 pins - one is the 12volt power in, one is a connection to ground, and one is the 'Acc' output.
When you switch the switch to 'On', the switch lights up by powering its bulb using the 12volt power pin and grounding through the ground pin, it then also sends 12volts down the 'Acc' wire to power whatever you want the switch to power;
So ........ have a look at this;
I've renamed the pins on your 3 switches with the pin 'names' - i.e. P=12volt power, G=ground, A=Acc
So looking at the diagram;
a) Each switch gets 12volts into its 'P' pin from your 'Multi Connector' which is connected to the Leisure battery.
b) Each switch is grounded to the chassis via its 'G' pin.
c) Each switch has its 'Acc' pin connected to the item it 'turns on' (i.e. the 12V outlets, the lights, the pump)
d) Each powered item (i.e. the 12V outlets, the lights, the pump) is also grounded to chassis to complete the circuit.
I've also made an assumption that the thing you had named as 'Splitter' is actually a connector to the pump and that this connector provides power and ground connections to the pump (as shown in my diagram, named as 'connector').
Finally - the item you have named as 'Fused Splitter' is the split charge relay that connects the Main Battery to the Leisure battery when the engine is running; The relay is triggered via the wire you have marked as 'Unknown' (which is usually connected to the Alternator signal wire so that the relay is triggered when the Alternator starts producing power i.e. when the engine is running)
Also, finally finally - you should probably have a fuse on each of the 3 power lines that go from your multi connector to each of the switches; and/or have a fuse at the Leisure battery on the wire to that multi-connector. That way the system is safe if you get any shorts/overloads.
Hope that helps/makes sense?
as shown in diagram I have made.
