I have had trailers all my life but they either didn't have brakes or had electric brakes.
This is the first boat trailer that has brakes, and I think they are surge brakes.
What is this in the picture circled in red? It is a hole in the tounge that the other piece, im gonna call it a key fits into. Backing it up the driveway without the key in makes the trailer brakes lock up, on flat ground it backs just fine with it in or out. Is that piece supposed to stay in all the time? Or just when needed?