It should be pretty simple. I've never done this, but it should work fine. Two wires off the spoiler; power and ground. You tie the power to brake like (+) and the ground (-). These should already be in the deck lid at the lights.
So, do you also need help with where to drill the holes?
If so, maybe someone with a spoiler has a template, or you can measure. Be careful to use an appropriate size drill bit, you dont want the hole too large.
I have an idea based off the car i car i pulled it off but i dont think i want to add the clips incase i change my mind later on and be stuck with those larger holes. The wires were cut off a few inches after the connector just leaving the red and black wires. May end up selling though if i change my mind after mocking it up today
i'm surprised i haven't seen where someone has cut out the middle post and rerouted the power thru the spoiler to the passenger side of it. Then you would only have 2 holes in the trunk. Would take a little bit of work and need a repaint though.
That is what i was thinking of doing to avoid another hole and run it through the right side, i was able to go back and get the entire trunk harness so can i just switch the harnesses to make it easier