The best place to go is a Ford dealership and order a real Ford service manual for your ST.
A distant second and third are the Chilton and other manuals that you can buy in parts stores. Some cover an entire family, and are mighty vague. Some are more specific, but still have multiple schematics for different years, trim levels.
Another unlikely source of information is the adapter plugs that you can buy at Best Buy and similar retailers with DIY car stereo sections. If you're lucky, the gizmo will come with a tiny 1 page wiring diagram that you can copy down on a notepad if you don't want to spend the $5 to have the part itself.
The factory manual will cost more than you probably want to spend, but it's by far the best.