Step one is to remove the amber (corner) cover, which can be done by inserting a flathead screwdriver into the seam between it and the main portion of the tailight. It pops loose, then you disconnect the socket from the cover.
Step two: remove the two screws that were hidden under the amber corner light cover.
Step three: find the plastic cover on the top of the light assembly (might be hidden by the trunk's weatherstripping). Pop it off and there's a screw to remove.
Step four: pull the taillight assembly gently out of the clips that should be holding it on. Pull straight out, no twisting.
