I got a quick and easy solution for ya. Just pack that thing up and send it to me, LOL. I'll wire it in on my car and show you how it works and then you can get another and copy what I did.
You are likely going to have to extend the wiring from the LED down into the trunk area and obviously make it long enough that it will not bind or anything like that when the trunk lid is open. But once you do that, you'll be able to ground it somewhere to the body/chasis in the trunk and then either connect the 12v source to the third brake light or even the tail lights for that matter.
How you will pass the wiring from the spoiler to through the trunk lid Im not sure, I would assume that there is a hole or something that you could use. I would assume the LED brake light has some current limiting designed into it but I dont know that for sure. If its an aftermarket or factory set up from another vehicle or something, I would hope they have the current limiting built into it.
