Update. Sirius and fm radio are working with car parked in garage and garage door closed.
Installation is very easy. Unscrew antenna whip. Set shark fin over the black antenna base, lined up and squared. Put masking tape around it to mark position. Remove shark fin. Clean area with alcohol . Heat with hair dryer( if car is cold). Use screw provided to tie pig tail to black antenna base, where you unscrew the whip. Take double side tap off of shark fin. Place over base where you marked it. Press firmly on front,then back for one minute each. Done. As I said there is a coiled pigtail that ties into black base, at the other end of the pigtail it ties into the shark fin. Where it ties into the shark fin there is a thin flat copper grid that is on the inside top that acts as the antenna.
Found a pic online. Looks similar to this on the inside. I have no worries about reception.