Do Not--I repeat--Do Not drop the plastic retaining nuts inside the interior trim panel!
Once you get the nuts removed, the locating pi will still be holding the taillight in place. Give it a good, firm tug, and the light will separate from the body. Then disconnect the wiring harness. Did I mention not to drop the wing nuts?
2012 Focus Titanium Hatch-6/12/12 Build Date-Tux Black-Charcoal Cloth-DCT-Winter Pkg-Moonroof-K&N Drop-in-Magnaflow 15072
2014 Focus ST2-9/9/13 Build Date-Perf Blue-Charcoal/Blue Recaros-Moonroof-Cobb Intake-Magnaflow 15155-QuickLifts