You need 3. As described before: 1 to the OBD for power, then you disconnect the throttle sensor from the pedal, plug 1 lead into it (the pedal), then plug the other lead into car.
This may not be exactly right as I dont have one, but the concept will be correct. The D1 modifies a signal from the pedal to the car, so basically is plugged in between the pedal and car.