I replaced my third brake like with an ten inch LED bar. Here's how you can do it.
The third brake light wires are light blue and black. It runs along the trunk lid. Snip the wires before the 3rd brake light connector and simply wire the spoiler's red (or white) wire to the light blue and black to black. If you still want to keep the third light, just rewire it the way it was, plus the new light wire, but make sure you cut far back enough to leave some slack to re-attach it. That should do it.
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ll <------------------------wire Honda light here
--------snip here
ll<------------------leave room to re-attach
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lllllllllll <------Connector
lllllllllll
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