YUP! That's entirely the case. The sharkfin is for GPS and Satilite radio (missing lead in my case) and the AM/FM antenna is in the rear window. You can access the lead by opening up the driver side c pillar.What you see is probably the GPS. Otherwise the fin is only used for satellite radio.
FM and AM antennas are in the windows. Both my S40 shark fins were just dummies. Nothing ran to them.
.I finally have an aux input even though I have premium sound.
I bought this:
and used this write up:
And I am pretty damn happy