Third brake light

Check the wiring harness where it flexes inside the trunk, the wires like to break inside the insulation and can be hard to find. Normally you can find the break if you pull on the wire ends, the break will show as an hourglass shape in the insulation as it stretches over the break. It is a common issue with trunk mounted CHMSL lights.

Thanks Steve. I was hoping you would say to replace the assembly itself because I can do that easily. I am not handy when it comes to car repairs, let alone electrical issue. In my experience, when I try to do the repair myself, I tend to make the problem worse and ends up going to a professional to get the job done. Is there a guideline to replace the broken wiring?

It depends on where you find the break. If it is on the side to the light then replacing it would work, but expensive compared to thirty cents worth of shrink tube and solder.

Wiring repair is not difficult. You need a way to remove the insulation from the wire, some heat shrink tubing, a soldering iron and solder. You can find all of that online or in most parts stores. I also like to replace the wire that broke with a new section, that is because, if it failed because of the flexing motion, is there another spot that is ready to fail an inch or two away from the current break? I do not like repairing a spot only to discover it failed a week later because I did not replace the wire.

As for how to do it, there are a lot of videos showing the various options from sealed crimp connectors to heat shrink and solder. These should give you an idea, they may not be your exact issue but they show most of the methods to repair the wires.
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https://www.youtube.com/watch?v=6EiIDNEiB_U
https://www.youtube.com/watch?v=rqHwVhSYZZ8
https://www.youtube.com/watch?v=aoD2aUvnQXg