Check the last picture in post 2 of the posting I mentioned for what folks may/may not have and you can see a tiny black button on the left side of that picture!
If you look at some of the other pictures posted, you likely see lots of wires and looking closer we may even see the two posts where some of the wires connect.
But to actually think of this as a resettable circuit breaker, we have to KNOW about it being a breaker as it looks like a simple connection point.
Only if we know it is there and then also know to look for the tiny black button on the side are we driven to look really hard at the side to find the button to reset!
Since the trailer group is left hanging out with less info like drawings to tell us how to trace the power flow, we can have a really hard time chasing power in from the battery to show us power gets there but doesn't go though!!
But I fully admit this may be bad info for your specific trailer as others have found!
If you have the metal box, try looking in the box under a bunch of wires for something many say looks like a microswitch. Find the breaker? Then search for the reset button!
If no box and no breaker, assume they changed it and I'm just messing with your mind!