Re: Trailor light question.
Connect the red wire (ground on the adapter, VERY non-standard) to the white wire (ground on the lights).
Don't trust the trailer to ground the connector wire or light wires --- just link 'em with two extra lengths of wire and rely on the ground system in the tow vehicle to do the work.
Most common failure I've seen in the many small boat trailers I've owned is grounding -- the wire gets corroded and fails to ground, lights then fail to work.
"The enemies of reason have a certain blind look."
Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.