I picked this to rewire an old trailer. Trailer lights often fail because they are grounded to the trailer frame and the ground connections corrode. With this set it grounds from the vehicle all the way to one of the trailer lights. You then have to send a ground wire from one light to the other. I also grounded the trailer.The set comes with a vehicle harness as well, but unless you have an old vehicle with a 2 wire system you will need a 3 to 2 (not 2 to 3) converter to use the included vehicle harness and get both brake and turn signals. Easier to just buy a 3 to 2 converter with harness like the Curt 56175.