Actually, according to the manual for the TRD
Spoiler install, that connector is supposed to be there for the spoiler LED.
Mine didn't work either.
So I routed the wire from the 3rd brake light through the interior of the hatch, and connected it to the connector that the old 3rd brake light on the roof was using.
It was hard to route it through the left inside of the hatch because there were already wires in there, and it's a tight fit.
So my friend brought some 75lb fishing line down, we routed that through the hatch, tied it onto the connector, and pulled it through the hatch to connect it to the other connector.