Remove the three nuts holding the taillight. Unplug the wiring harness on the back side of the taillight. Now you can move the housing around so that you can un-hook the wire (push-pull rod) where it connects to the red plastic lever on the back of the lock cylinder. There's no need to remove the red plastic lever from the lock (nor is it easy). Now you need to slide the U-shaped metal retaining clip out from the back side of the lock. At this point I usually rotate the lock cylinder 180 degrees so the red lever is pointing up instead of down. That makes it easier to jiggle the lock assembly out through the hole.