Running lights on trail tech utility trailer

Question:

Looking to rerun wiring with new rear lights currently Peterson and will use exact replacements. My wire runs through the tubing with the yellow, yellow/brown and same for green, green/brown. My question is I see the wire coming in and out the different tubes to the back and they bypass my running marker lights. But out of the back there is a 3rd black wire coming out on each side which isnt there at all the ins and outs. Would the black wire be running from my taillight a back up to my marker lights? Im really confused where this extra black wire comes from. Thank you.

asked by: Larry K

Expert Reply:

The only way to know for sure how the side marker lights are wired is to take one loose from the trailer and check the wires on the back of the light to see what color it is.

I have attached a drawing that shows how trailer wiring is typically run. As you can see the green wire is for the right hand tail light and the yellow is for the left hand(driver side). Chances are that the black wire is used for a light bar or license plate light.

The easiest way to find out is to use a circuit tester like part # PTW2993 and run through the functions with the trailer connected and see what each wire is used for. Or you can use a 12V battery and test the trailer wiring with the trailer unhooked form the tow vehicle.

expert reply by: Jeffrey L