Yes Jack it is for the interior lights.
Good, so now, I have no good guesses on why your outside lights don't work.
I lost my left hand brake and turn signal, because a mouse or rat had chewed through the wire, somewhere behind or under my refrigerator (before I mouse-proofed my trailer). I spliced in a new section of wire to bridge that gap and things are fine now. Do you have mice where you live? (Stupid question I guess, kind of like, "Is the Pope Catholic?").
Anyway, the wires to those outside lights are in the wire bundle that goes from the bottom half to the top half in my bathroom. They are joined in that bundle by wire nuts. You can separate them (one at a time by removing a nut) and then test the lower half end for voltage using a multimeter. If you get no voltage, you know the break is somewhere between that point and the front of the trailer.
You can also check for voltage at the connectors on the side of the battery box with the trailer hooked to your tow vehicle and something like a turn signal activated. If there's voltage there, the break is between it and the wire nut point.
But, if there's no voltage in the front, there might be a problem in your tow vehicle. I've bought (online) a simple plug-in, 7-pin trailer plug tester. It has lights in it to show if each circuit in the trailer plug is good. I think this is what I bought: https://www.amazon.com/CURT-58270-12V-Connector-Tester/dp/B001EOWQY4
- Jack