Connect the electronics to the motors and batteries. The motor drive board has 1 connector for the main battery power and 1 power connector for the 80mm cooling fan that I would highly recommend you install directly above the mosfets. There is spacing for some long skinny bolts to hold a cooling fan. I bolted the motor driver above the Arduino breakout board to save space.
Also, you might want to use some smaller wire coming from the batteries to power the Arduino board, as the 10ga wire I used for main power and motors is a bit overkill for the microcontroller.
I installed a 30a 120v toggle switch from Radio Shack to switch the main power ON/OFF, this is my kill-switch. I also found a terminal-block for power distribution at Radio Shack for a few bucks. It is the white thing that all the wires go into in the pictures. This makes removing the electronics a whole lot easier.
It is very important that you wire everything up correctly. Otherwise you might blow up the motor controller.
So make sure that you check the code before connecting anything to verify that you haven't mixed any wires up.