Stay away from FM transmitters, if you have to use an FM adapter make sure it comes with the male and female antenna plugs,
I did the installation for my cousin in a 2005 Ford Excursion Eddie Bauer
and to find out if you can add the pie aux interface, your radio needs to have external CD changer controls or the RSE rear dvd input, to test for external CD controls
insert a disc and after a few seconds press the the CD button the radio needs to display NO DJ or NO CD in this case you can use the PIE FRDN-AUX