My spoiler was wired to the left side (driver side) brake light. It was the closest to the spoiler wire harness.
It is very easy. The trunk lid cover is the only thing you have to remove. If you look up under the rear deck you will see the plug for the brake light and you will see how to feed the wire through the deck from the hinge to the plug.Sounds like they are easily accessible. I didn't look in the trunk yet but thought they would be all covered up and such. Did you have to remove coverings besides the trunk lid cover?