The purple box is the DC motor speed controller. It's made by Auburn Scientific in Auburn, California and is capable of delivering 190 horsepower to the motor (140kW). A liquid pump shown in the center picture circulates coolant from a reservoir, through the aluminum baseplate of the controller, to a small radiator ( shown in picture at the right) behind the grill, and back to the reservoir. I purchased the pump from Randy Holmquist of Canadian EV's and it really nice because it's so quiet. The radiator came from the cab heater. Now there's a 1200 watt resistance heating element (from Randy also) in it's place.