Located behind the plastic panel underneath the back passenger's side window. I discovered this while pulling the Onstar antenna off and following the leads. You can see it if you pull the trim panel back that's on the right side of the back door.

jerij

wait a second...it's in the door or the rear hatch area?

-wC

Ooops! Pull the right side panel off the back of the HATCH door area. There is a black ring holder with a black bolt that is also holding this panel on.

jerij

I'm guessing this panel right here held on by two bolts?

http://img.photobucket.com/albums/v167/wildeone81/Chevy%20HHR/IMG_5566.jpg

-wC

I'm guessing this panel right here held on by two bolts?
-wC

Yep, maybe this picture will offer additional help.

http://n8zcc.com/pics/HHR-XM-Loc.gif

Wow! Thanks Monster!

jerij

Anyone know where I can get extension cable to make use of the factory antenna with my Roady2?

Try xmfanstore.com.

Charles