If it's factory then you should just need to buy a wiring harness for that specific brand of Ford. The harness should take the deck that your installing to the amp.
My truck has a Ford Premium Sound System, which is an amp seperate from the stereo. If I need to bypass that, I will need to know how. The stereo I am installing is a JVC Car KDG140 50Wx4 Mosfet In-Dash CD Receiver.
If it's factory then you should just need to buy a wiring harness for that specific brand of Ford. The harness should take the deck that your installing to the amp.