Quote: Originally Posted by joego
Onstar isn't GPS though; you have voice communication with the people at OnStar. I suppose the antenna on the thing could be a compound antenna with GPS and OnStar recievers built in, but good luck in you project and for god sakes tell us what you did to make it work.
Actually, from what I remember, Onstar is simply a GPS reciever and a Cellphone jammed together. In the newer, digital versions, there's also a databand in the cellphone that allows two-way data between the car and the Onstar service.
'Onstar' isn't exactly some mythological third service that exists out there. It's GPS and cellular.
As for the antenna: Generally GPS antennas are GPS antennas. There's no seperate GPS signals that prevents one GPS antenna from working with one reciever and not another. It's not like trying to use an FM antenna with an AM radio.
You should be able to find the Onstar brain and unplug the GPS antenna from that, adapt it and extend it to your headunit. Finding an extension might be a bit of a pain though, I don't know how common those are.