i did this same thing in my dodge and luckily its the same thig on my ford. just wanted to post this for anybody wanting to use an existing subscription for theyre truck instead of buying a new one.
a place called citruscables.com built me this custom cable and it has worked flawlessly for over 4yr in my dodge and ive already tried in my ford and it works great.
i got this one 8ft to be sure it was long enough (actually its really too long 4ft would be plenty. it has a SMB jack on one end and a SMB plug on the other. i found the 90* end works great for giving the cleaner look not having the wire going stright and curving back (just IMO).
the next step is far easier in this truck than my dodge. locate the OEm sat radio box under the dash, its almost right where the OBD port is on the drivers side and right where te AUX switch panel wire harness is, youll see the single wire with a yellow plastic end pluged into this box. simply unplug it and plug the cale into it, then the other end to the docking station.
much easier and cleaner than running another antenna and having somethign else on youre roof.