You can actually see the 3rd brake light, or just some glow from it? I thought all the cruisers had the light in the same place. I can see a small glow when I hit the brakes. Check the inside panel that covers the light on the inside of the hatch. Maybe it came loose. It's held it by a couple of clips on each side. Just hit it easily with the palm of your hand to make sure it's tight against the window.
