Trailers longer than 15 feet and heavier than 1500 lbs must have a brake system that means another circuit for hydraulic brakes. Trailer electrical connectors come in a variety of shapes and sizes.

5 Wire Flat Trailer Side Plug
Wiring trailer lights 5 wire. Video tutorial on how to wire trailer lights. How to wire trailer lights. Some vehicles use a combination bulb dual filament for turn and stop. Tow vehicle taillight wiring 2 wire system. The trailer wiring diagram shows this wire going to all the lights and brakes. By reducing a 5 wire to a 4 wire you eliminate the connection for the trailers brakes.
The left brake wire and left turn signal are yellow. A trailer with a 5 wire harness has connections for marker brake and signal lights as well as an electric braking system. 5 wire trailer wiring diagram. Trailer wiring color code explanation. 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. 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.
Adapt the 7 way trailer socket on your vehicle to work with a 4 way or 5 way flat connector on the traileradapter also provides a 12 volt power source outlet. Side marker lights are powered by the brown wire. White ground wire. This is the general configuration upon which 5 way 6 way and 7 way wiring systems build upon. Green right turn lightsbrakes. Be sure to check with your local law.
An extra pin allows using another extra function. Not all trailers have reverse lights so consider your own trailer as you wire in a 5 way plug. Versatile adapter and power socket adapts from a 7 way rv blade trailer connector on the vehicle provides a 5 wire flat 4 wire flat and a 12 volt power socket covers included to protect. Brown tail lightsrunning lights. So here i have an older trailer which needed some work along with re wiring the lights. Also it must connect with things if included that use the aux power and back up lights too.
The basic purpose remains the same whether your truck and trailer is using a 4 way 5 way 6 way or 7 way connector. By law trailer lighting must be connected into the tow vehicles wiring system to provide trailer running lights turn signals and brake lights. As an example you will find another blue wire in a 5 way system that powers auxiliaries like the electric brakes. Yellow left turn lightsbrakes. Tow vehicle has same bulb for lighting stop and turn signals. If your trailer is significantly heavy and is at the upper limits of the towing capacity of the vehicle.
White remains as the ground. 5 pin trailer wiring is very similar to 4 pin wiring but it adds in a blue wire for the reverse or backup lights. This is a fairly simple setup no license plate light or clearance lights. Use a simple 4 way flat connector to power your 2 light trailer lights or use a custom vehicle specific trailer wiring harness.