When you hook the switch up pin 1 is 12v supply, pin 2 is the load, and pin 3 goes to the - output of the dimmer. The + output of the dimmer is not used. The Input + and - of the dimmer need to be connected to your lighting power source and ground. Be advised that this dimmer pulls power in the off state so you need to be able to isolate power from this circuit when the aircraft is not in use.
Nice thing about the dimmer is that it has an off position and has a slight resistance to rotation. Also comes with a black and a chrome knob so you can pick which you like.
Regards
Jeff