This is a few years late, but because I just added a brake controller and 7 pin trailer plug to my 02 Sport Trac so we could tow our tent trailer (2300 lbs), I thought I'd share the experience to help others whose STs came similarly equipped (sans towing package).
The most difficult part of this job is running the wires back from the plug to the battery, but the job itself is straightforward.
I found everything I needed at Princess auto for about $225.00. This included a Hopkins Agility brake controller, Hopkins 7 pin/4 pin combination plug with mount, four 25' spools of wire (black 10 ga., Blue 10 gauge, red 16 gauge, white 10 gauge) colour matched to the brake controller, 20 amp inline circuit breaker, a 40 amp in line circuit breaker, wire loom to keep the wires wrapped up together, crimp connectors and shrink wrap. E-trailer.com has a good video that details how to run the wires between the controller, battery and brake light wire (which is light green, not green/red). You can find that here:
http://www.youtube.com/watch?v=OQsbboVwOKs
I started at the back of the truck and let the spare tire down for more room. I then mounted the plug using the metal bracket in the kit and connected the existing 4 pin light harness to the 4 pin connection at the back of the new plug. After that, I connected the black wire to the black wire on the plug, the white wire on the plug to the frame for ground, and the blue wire to the blue wire on the plug. Once the wires were crimped together and shrink wrapped, I wrapped the entire length in the 3/8" loom to keep it all together. I ran the two loomed wires (I didn't connect the purple, as our trailer doesn't have reverse lights and I don't know of anything I'd be pulling with the ST that would) along the frame rail using plastic clips and self tapping screws, being careful to stay away from exhaust, steering and suspension by running alongside the fuel lines before coming up through a hole near the front of the truck at the engine bay. I mounted the 40 amp circuit breaker and 20 amp circuit breaker using self tapping screws to the inside of the engine compartment alongside the battery and ran the black wire from the plug up to the aux terminal on the 40 amp circuit breaker and some of the remaining black wire from the "battery" terminal to the positive terminal on the battery. I should mention at this point that it's much easier to do this with the battery out of the truck, and it should remain disconnected until the wiring is finished. Take the rest of the black wire and go to the inside of the truck. There is a rubber grommet under the dash in the firewall that you will need to cut so you can get three wires (controller, Hot and Ground) through to the brake controller. Take the remaining black wire and poke it through. You'll need to guide it past the brake booster housing by peeling back the plastic fender cover beside the drivers side front wheel. Use zip ties and clips to keep the wire from interfering with steering and suspension components, and run that wire to the aux side of the 20 amp breaker just installed, and some remaining black wire will also go to the positive side of the battery once it is back in. You'll also want to run the blue wire you ran along the frame through this same hole to the blue wire on the brake controller, and the white wire through from the brake controller to the negative terminal on the battery. Using the 3/8" loom will keep these wires together will help keep everything together and match the rest of the wiring on the truck. The next bit is tricky, as you will need to determine the correct wire for the brake light switch (light green on mine) and use the red wire and a quick splice connector to tie into it. You have to make sure that the wire you are tying into only comes on when the pedal is pressed, otherwise you can easily fry the controller by using one of the other wires that is always energized. You will then need to run that smaller red wire along with the three other wires you just ran through the grommet to where your controller will be mounted. Note that the adjustment buttons for this controller are on top of the unit, so you will need to find a spot that allows you to adjust the settings before you use the supplied screws to mount it. Then it's a matter of matching up the wires by colour, crimping them together wrapping everything together. Connect the white wire to the negative terminal, the two black wires from the breakers to the postive, and you're ready to go, assuming you've put on a receiver hitch.
I'll post some pics here shortly if anyone is interested. The video on e-trailer is for a different controller, but the set up is exactly the same.
