I got the kit that included all the right connectors so I did not need to cut and splice anything, and could take it all out if needed.
problem with any car with separate lights for turn signals is you need to somehow combine the brake and turn lighting into one bulb that trailers usually have. to do this you need at least the block box you see in your lower photo. by the time you get the harness and the box you might as well buy the proper kit.
This kit are not perfect though. My trailer has crappy wiring and can short out the bulbs at the rear I have found. It killed my black box in the $30- kit I had in. Now being an electrical engineer that just put me to the challenge of designing an building my own black box with protections against short circuits. I have tried fixing the old trailer, but this was easier.so I use the kit with all the nice connectors that match the Honda plugs, but my own box that turns on the trailer lights with brakes, with turn signal, and when they are both on the lights go off so there is braking and turning always indicated. I also used N-ch FETs instead of diodes or bi-polar transistors. less voltage drop. runs cool and bulbs are brighter.