Recommended Testing Method to Determine Trailer Wiring Functions

Question:

my trailer has 1-green wire,1-green and brown wire, 1-brown and white wire, and 1-white wire. the standard color code lists a green,brown,yellow,and white wire. can you tell me which color on my trailer goes to the left,right,and tail markers,i know the white is the ground. thanks for your help

asked by: Dan

Expert Reply:

Usually a 4-pole trailer connector will have a white wire as ground, green wire for right turn/stop, yellow wire for left turn/stop and brown for both sides' running lights. But since there is no real standard for wire color on trailers (and since colors can sometimes fade/change after exposure to weather) your best and easiest solution is simply to apply 12V power to the wires one at a time to see what function becomes active.

You can use a vehicle's 12V battery or a spare - if like me you have one in the garage you trip over occasionally. Simply attach the white ground wire to the battery negative terminal and then one by one connect the other wires to the positive terminal. You can have a helper watch the trailer lights while you do the testing to determine what function each wire carries.

The linked article on trailer wiring may be helpful.

expert reply by: Adam R