If it was mine I think I would start from scratch. Most of us bought our trailers used and it's anyone's guess who the previous owner was. Too many well intentioned previous owners don't necessarily go by the book when it comes to wiring. I would trace each wire to the target (what its purpose is) that it supplies. EG: separate each of the trailer towing lights and tag them. Lights: left, right, marker. Brakes and 12VDC.
We all know that some people will use what ever wiring they have hanging around and while it's hooked up correctly, the colors of the wires are not in theory or code. A leftover green is poor example for positive (just saying).
Open up the compartments inside the trailer. I think Mainah is correct but it's important for you to know your trailer and where everything goes. Once you figure everything is correct and in its place then you can make a list of wiring or plumbing and adhere it to inside a cupboard door for future reference. Understanding your wiring layout is an asset for you.
This is also a great opportunity for you to check the connectivity of the wires to each other. Are there any twisted wire connections (ewwwww)
Use proper connecting methods. Many of us here prefer soldering and heat shrink. Even crimped connections are fine but still solder and heat shrink when and where possible. Avoid using electrical tape because most of the time it doesn't stick the way you want it to. Butyl tape tightly wound is best, better insulation and keeps moisture out (for the most part)
Jerry & Debbie
Ford Explorer 4.6 Triton V8, AWD, 4x4
1985 Sunline Saturn T-1350
Ham radio VE3JCJ, VHF, UHF and HF