with my grand prix.. there was an orange wire that connected to the back of the stock head unit on a separete harness. That wire had to be connected to my remote lead off the new head unit. I assume its the same situation, but you'll need to find out which wire it is. Shouldnt' be too hard //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
i believe in fords you are able to use the existing amp...i personally would bypass the amp b/c with the extra wattage coming from new stereo, it will blow your amp in no time...
Generally you're suppose to replace everything(headunit, amplifier, speakers, wires) when you're dealing with one of those factory premium systems. Even if you get the new CD player to work with the factory amp the speakers are still being powered by the factory amp so it won't sound any better or louder - it'll just sound different.