Servo motors have 3 wires as they expect a special signal called a PWM signal. Servos are a special motor that send feedback back to a controller. This closed loop system allows a controller to tell a servo where to go and the feeback lets the controller know it got there; and to make adjustments as needed. Its for precision. Which, if you were just wanting to turn a motor off and on with digital outputs, doesn't sound like you need the precision. Why not just use a standard DC motor. You can find them cheap at any hobby shop or even Radio Shack. If you are stuck on using a servo, you will need a servo controller from phidgets, which works very well and is even cheaper than the 8/8/8.