If you break a plastic clip, twist in place a new one with a pair of pliers (clockwise). Make sure that it can move freely.

Not like this...

...but like this.

It is possible to attach the brake light right onto the rear window, but it is better to attach it to the plastic cover.

1. Take out the left taillight (two screws and take it out very carefully).
2. Remove the cover on the left D-post: Take out the lamp (tilt it out on the left side with a flat head screw driver) and unscrew the bolt inside, take off the gas damper (insert a broomstick as a support under the tailgate), two plastic clips (insert a long screw driver and bend out).
3. Release the side cover at the rear (two screws).
4. Glue the brake lamp onto the plastic cover at the top, close to the rubber seal.
5. Remove the plastic cover (two screws + four plastic clips).
6. Drill holes from the inside of the plastic cover and into the feet of the brake lamp and put in screws.
7. Cut a notch in the edge of the plastic cover (or drill a hole), put duct tape on the wire and put it through the notch.
8. Connect the negative lead to ground (rear wiper).
9. Pull the plus wire down to the left taillight: First through the plastic sleeve (use a thin string to pull it with), then fasten with tape on the D-bar, then through a hole (put a plastic sleeve on the wire here) and into the room where the taillight is located.
10. Connect the plus wire to the brake light circuit (strip both wires, twist tightly, solder, and put on plenty of insulation tape).
11. Mount both plastic covers, side cover and left taillight.