Help with XM radio
 

My fiance and I have a 2008 LS with OnStar installed, we don't have the XM package, but her brother has a 2008 LT2 with OnStar/XM. He pulled out his head unit and installed an aftermarket and set it to use his Sirus package that he was already paying for. He gave us his head unit and said that if we could figure out where the XM receiver is, he would give it to us as well.

My questions are:

1. Where is the XM receiver?
2. What do I need to do to keep his working with the OnStar system, does it use the same antenna or wires?
3. Do I need to run any additional wires to plug up the receiver?

Thanks an advance!