you have to run a wire form the back of the headunit to the the green Vehicle Speed Sensor wire connected to the PCM under the hood.
http://www.grandprixforums.net/threa...05-08-with-HUD
seems there has been a lot of question on this specifically (pin location on either end) next time I open my dash I will get apic and also os the VSS on the PCM. without the VSS wire your GPS will never actually function properly with identifying its own location and also putting directions on your HUD which is the other benefit of the factory nav unit.
