trailer wiring isnt too bad, just have to isolate the issue... the first thing I would do is get a voltmeter, and verify you have voltage to the proper poles on your truck plug. if you feel like tinkering with it before the dealership: I would look and see if there is a junction box where the plug harness goes into the individual wires that run throughout the trailer. If there is a terminal box it could be easy enough to check for wiring config, some newer trailers use a molded plug, but if it is not molded you could take the plug apart and verify wiring on the trailer plug colors match the schematic for industry standard... colors are not 100% either, some swap a couple around, but would help to know this if it is the case. take a look at the wires going to the loading lights, the color supplying them should stay the same throughout the trailer, and then check that this wire makes it to terminal... if I am in doubt i use a battery charger or other power supply to apply voltage to individual wires and see what lights up.
All it takes is time and patience, and a mulitmeter helps.