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Standard Color Code for Wiring Simple 4 Wire Trailer Lighting  


I have had to mess with trailer wiring for years, once or twice a year anyway, and I just cannot keep the color code right, ect white/ground, brn/ running lights, grn/ right turn, yellow left turn? Please help me get it right. thanks


Expert Reply:

You have it right so far, the 4-way connector is just as you have stated. Remember that Yellow has a L in it so that is the left side brake/turn signal and green has a R in it so that is the right side brake/turn signal.

The colors for wiring a 7-way connector are as follows with the 4 colors of the 4-way connector remaining the same.

Brown-Tail/Running Lights
Green-Right Turn/Brake - Remember green has an R in it
Yellow-Left Turn/Brake - Remember yellow has an L in it

Blue-Brake Controller Output
Purple-Auxiliary 12v Power/Reverse Lights/Reverse Lockout For Trailer Brakes
Black 12v Battery Power

I have posted a link to our FAQ wiring page for more detailed clarification.

expert reply by:
Bob G
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Bob O.


1995 GMC C1500, the OEM trailer harness has all the standard colors plus a lighter green, five total. Can I assume the lighter green is backup lights?

Etrailer Expert

Jon G.


That's a safe assumption, but I recommend testing it out with a circuit tester like part # PTW2993 just to be on the safe side of things.



I have two amber and two red side marker lights for a boat trailer. This is an older 1999 trailer. The existing lights had one wire connected and it’s the brown wire (4-pin) 5 wire. The replacement lights have two wires red and black. I currently only have the brown wire exposed. How do I wire brown wire to this light.

Etrailer Expert

Chris R.


You will need to find what functions the red and black wires on the new light are supposed to carry. There should hopefully be a label on the wire itself or at the back of the light housing where they connect. It's possible the black wire is for ground while the red wire is for power (which is what you would connect to the trailer brown wire) but you'll want to try and verify this.



I don’t have a white wire coming out of my Chevy 2006 pick up. Red black and blue are the three big wires then ther are five other I want to hook up a flat 4 prong hook up to my trailer which wires do I use my trailer connecter has four colors green Brown white and yellow what goes where!!!!

Etrailer Expert

Chris R.


You'll need to test the wires coming from your truck individually for function. Use a circuit tester while you have a buddy turn on each of the lights in the cab, locating which wire shows power with each function. You will then be able to match them up to the 4-Way harness. I'm not able to track down a wiring diagram for your Chevy truck.



I have a separate wire for brake lights. How does that connect into a 4 pin connector?Thanks for any help

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