I used the same lights as you 3 years ago, still going strong. Only difference is I took the connection from the Kurt plug from the back side of the trailer plug so as not to cut into anything OEM. I did use some Posi-lock connectors I got from Amazon, Di electric greased all the connections as I taped and put them back together. Put everything in lumes, taped and wire tied everything up out of the way.
Ive been following along here. Seems you may have some sort of short/loose connection that went away when you pulled it apart. They are a nightmare to deal with. Could it be mice munching on part of it? At this point you might be just as far ahead to go ahead the rewire everything from scratch and call it a day.
The mice thing has caused me to slug it out with a couple of boat trailers along the way. I understand your frustration.
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