My Rockwood Mini-Lite has a 7-pin plug but no backup lights. I added two of (Amazon) on the rear below the bumper. They light the area well. (The product in question is unavailable but there are many alternatives.) I had to add the power wire to them and connected it to the backup light wire in the umbilical, which was capped off near the front of the trailer.

Your query reminds me that one of them hasn't worked for awhile. I suspect the wire to it was damaged. It's unlikely the light itself failed because they're a sealed unit. I haven't gotten around to fixing it because I so rarely drive the trailer after dark now that I'm retired. It's on my list.

Depending on your placement options, you may wish to consider replacing the existing tail/brake lights with some that have integrated backup lights. That assumes that the extra wire exists, or that the path to add a new wire to the existing location is accessible. My choice of location cuts off the top edge of the light beam but it's very bright, anyway.