Well I am still waiting for GMPartsDirect to send me the GPS Antenna. What I am wondering is if I go ahead and upgrade the LUX amp and install the Nav head unit will the radio part work. I have an chance to get by the dealership tomorrow if needed to clear the theftlock, so I would like to upgrade those two pieces tonight. I figure if/when I ever get the parts from GMparts direct I can add the antenna as well install the CDX. I know the Navigation functions won't work without the antenna, I just don't know if the head unit will work without it plugged in. Will it come up with an error saying no antenna connected and not let me do anything else? Or will it function as normal just won't have GPS capability? Thanks for help