Trailer wiring information/diagrams

In the following tip, I will show the diagram for a square connector, round connector and the trailer wiring diagram.

I always connect the ground wire at the vehicle and the trailer side. Many people don’t and end up having intermittent flashing lights problems. I had too many of these problems and want no more. One time the flashing lights came up behind me and pulled me over. I did not get a ticket (this time) but was to to fix the trailer as soon as I got home. Ergo, I now use the ground wire, it’s easy to install.

Here is the diagram for the trailer. Note there are a total of four lights. Two stop/running/turn lights on the back and two side running lights. The right side of the trailer has the BROWN and GREEN wires while the left side has teh BROWN and YELLOW.

BROWN – wire are used for the running lights. They go to each of the four lights and cause the lights to come on when you turn on your vehicle lights.

GREEN – This wire is used for the right hand turn and stop lights.

YELLOW – Yellow is the left hand brake and turn signal.

WHITE – Ah, so you noticed there is no white wire. Well to let you see it, I colored it BLUE. I tried to show it as white but no one could see it with the white background.

Round trailer connector diagram.

In the following diagram, I have numbered the pins:

  1. Electric brake pin
  2. Auxiliary pin – not normally used
  3. Right turn and stop pin
  4. Taillight or running light pin
  5. Ground pin (use it)
  6. Left turn signal and brake light.

Rectangular connector

Troubleshooting guide

No lights light up 1. Bad ground
2. Trailer harnes unplugged or bad connection
3. Vehicle’s running lights off
Lights on trailer do not match vehicle lights 1. Trunk harness not wired properly
2. Trailer wires not wired correctly
A specific light does not light or flickers 1. Light bulb is bad
2. Wire broken
3.Bad wiring connection
All lights flicker 1. Faulty ground – getting ground through trailer ball
2. Bad ground wire
Vehicle fuse blows 1. Trailer wired incorrectly,
2. Bad light socket
3. Wire pinched through insulation and grounding out on trailer frame.