What size wire should I use to extend the wires on the control box, to connect to a 12V power source?

You may use any 16-18 Gauge Automotive grade wiring if you are needing to extend the control box wires.  Please note that any other wiring besides the power and ground should not be modified, and will not be covered under warranty if any wires are cut other than the red and black power wires for the control box.