Here's a photo of my one battery.
There are four wires and marked.
Since you only have two red wires and one has a breaker, the one with the breaker is for a power winch (or possibly a power jack). Other red wire should to to the large splice and into the breakway switch (if you have electric brakes), and to the converter inside the trailer and the tow vehicle.
(Disregard the other red wire; that goes to my second battery, and the black wire that goes to a Trimetric meter inside the trailer.
The black ground is to the winch, the white is to the trailer frame.