I wired directly to my taillight and brake light wiring for my harness and it ran the lights on my harbor freight trailer just fine. My Elise was an 05, not sure if that matters.
If memory serves correct, I think I may have gotten a box that converts the individual brake/tails that the Elise has into a combined signal needed for my trailer.
Something like this:
Tow Ready Part tow119130 - Tail Light Converter - - 4 Wheel Parts