Some trailer builders just connect this wire to the frame then connect the ground from all the other lights and accessories to the frame as well. And the third diagram using clearance lights.

How To Rewire Your Boat Trailer Boating Magazine
Led trailer lights wiring diagram australia. One clearance light on each side and then one larger one at the back. As for brake light either pin 5 blue wire or pin 6 red wire reply. These too would run off the brown or parking light wiring same as the license plate light. Utility trailer 03 4 pin trailer wiring and diagram duration. 5 way trailer wiring diagram allows basic hookup of the trailer and allows using 3 main lighting functions and 1 extra function that depends on the vehicle. An extra pin allows using another extra function.
The trailer wiring diagram shows this wire going to all the lights and brakes. 5 wire trailer wiring diagram. I have attached a helpful article that explains trailer wiring. 7 pin ebs trailer wiring diagram. Led trailer lights with non standard wiring. The license plate light would run off the parking lights known as the brown wire so you can pull the power supply from either side.
If you have a separate wiring system on your vehicle you can use part rm 732 which will take the separate wiring and convert it to a 2 wire system needed for the led lights and pigtail. The lights wiring also need regular maintenance. Heres the wiring diagrams showing the pin out for the plug and socket for the most common circle and rectangle trailer connections in use in australia. Also it must connect with things if included that use the aux power and back up lights too. I put this here because i had a hard time finding and figuring this out for my trailers. Since january 1st 2015 all new trailers exceptions apply need to comply to adr3804 that specifies they have either anti lock brakes abs or an electronic brake system ebs to automatically adjust the brakes.
Firstly you need to check all the lights are working every time you hitch the trailer to your car. How to maintain the led lights and wiring on your boat trailer. If you have been boating for any length of time you will know that your trailer and its lights need regular testing and maintenance.