There is rarely a wiring diagram supplied with any trailer. The driving lights are a pretty standard thing, and the supply to the trailer components/fixtures can vary from one trailer to the next.
Like Bob said, it is often easier to rewire, than to sort out what is there. Plus, you can then have the confidence that everything is okay. You do need to have a good basic understanding of electricity too, but that can be learned. Buy a new 7-pin pigtail to lead into the trailer, and run new wires from there. Here is a drawing that shows where various wires go to. It is quite simple, if you know your stuff.
I have never wired a trailer with backup lights, but you can use the aux circuit for that. The license
is put on the marker light
You can add a battery
too, most put it on the tongue as it needs to be ventilated for gasses. How do you intend to charge the battery, other than when it is hooked to the vehicle? The battery needs to be fused, as well as the distribution lines to the individual draws (lights/pumps/fans/etc).
I prefer to return all the circuits with a wire back to the negative connection, rather than rely on the frame. It is a wee bit more work, and a small cost, but I have seen too many problems with the frame connections corroding.
If the trailer is equipped with brakes
, you do need to ensure they are wired in correctly, and will need a brake controller installed in the tow vehicle.