What are the Wire Functions on Trailer Tail Light # ST40RB

Updated 02/21/2012 | Published 02/16/2012

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Question:

when installing my trailer light kit, i connected the brown and yellow light to one light and the brown and green light to the other light and white to ground. all the lights work except my running lights. I think the directions said to spice the green wire with the brown wire? I did not do that step? should I ? I do not thin its a fuse because the light on the truck still work.

asked by: James

Expert Reply:

Trailers have tail lights that have a combined brake and turn signal on the same circuit. For light # ST40RB as an example, the green wire carries right turn and brake lights. The brown wire is only running lights. It sounds like you attached the brown and yellow wires on the tail light to the brake and turn signal wire from the trailer connector.

The trailer connector at the front of the trailer should have 4 wires coming out of the back of it. The covered pin is the ground wire. The pin next to it is the running light wire. The next wire is left turn signal and brake. The last wire is right turn and brake.

But, some 4-Ways actually have 5 wires in the back, a wishbone harness. In this case there will be a wire that is brown with a yellow stripe, that is the running light circuit for the left side. There will also be a wire that is green with a brown stripe and it goes to the right tail light. These wires attach to the brown wire on each respective tail light.

If your harness has a different style connector, connect the trailer to the tow vehicle and then test the wires behind the trailer side connector using a circuit tester like # PTW2993, to determine the functions.

expert reply by: Michael H