very few trailers have bu lights, shame actually
I installed them on a previous trailer, haven't done the new one yet
I just installed to inexpensive so called "driving lights" and ran them from the yellow wire through a relay mounted on the tongue. power for the bu lights actually comes from the trailer battery. the relay is energized by a feed from the truck's bu lights via the yellow spare wire
my thinking was that the trucks bu light system wouldn't be adequate to feed 2 high wattage lights on the trailer
bu lights are great for two reasons, seeing when backing after dark and a warning to other drivers especially in gas stations