Just be aware the when mounting BACK-UP LIGHTS on the rear of your trailer they have to be DOT APPROVED type otherwise you will most likely fail your DOT SAFETY INSPECTION and have to remove them... The LENS of the back-up light should have a DOT NUMBER stamped into the lens... This is the way it is in our Virginia DOT SAFETY Inspection Stations at any rate...
Mounting side lights on the trailer frame near the rear of trailer will not come under the same DOT RULES as mounting them on the rear of the trailer.
Actually for us the side mounted lights are better as you can't view directly behind your trailer anyway. My 5th wheel trailer has the two 7-inch scare lights mounted up high on the rear side of our trailer. These guys light up the neighborhood when being used... I just turn them ON when backing up...
On my OFF-ROAD POPUP the BACK-UP lights wiring is terminated in the 7-way Electrical Junction Box where my trailer hookup cable is terminated and is covered with one of those large YELLOW twist-on connectors. The BACK-UP lights wire is PURPLE in color but I imagine this color varies with the different manufactures on the 7-way trailer hook-up cables. When connected to the truck trailer connector I do have 12VDC on this wire when in REVERSE and with my 2010 Ford Truck Ignition Key turned on...
Roy Ken