Red, Black, and White Wire Functions on Old Trailer Light

Question

Question:

Hello I have a stop and tail light that needs replaced. I have purchased a light and my camper trailer has a red, a black, and a white wire. The light I purchased had a green, a rust colored wire and a spot for the white ground screw. Can you please help me understand my wires please.

asked by: Shirley G

0

Expert Reply:

It is likely that the red wire on your old lights is the turn signal/brake light wire, and the black wire is the running light wire. That would make the white wire the ground. You can verify this by testing the wires using a circuit tester such as # PTW2993. Connect the trailer to the tow vehicle and have someone operate the light functions while you test the wires.

On your new light it sounds like the green wire is turn signal/brake light, brown is running light, and it grounds through the mounting hardware. You could crimp a ring terminal to the end of the white wire so that the mounting hardware can go through it to ground the light.

expert reply by: Michael H

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Donald T.

5/31/2020

Can you please tell me the light has 3-wires? The red is + positive? right? The black is - negative? right? What is the Yellow? Thanks

Chris R.

6/3/2020

It likely isn't a simple power/ground configuration. If I had to guess, I would think the red wire is for stop/turn signal, the black wire is for running lights, the yellow if for reverse (maybe), and the light actually grounds through the mounting hardware. But that's just a guess - if the wires aren't labeled in any way I HIGHLY recommend actually testing them by applying 12V power to each wire to see which bulb it illuminates.

Donald T.

6/3/2020

@ChrisR Great suggestion, I didn't think of testing it, Thanks my hunch is there are only 3 wires; red, black yellow, it's an aftermarket center brake light; designed to be mounted under the bumper outside, so the red is for brake light, black is ground, and yellow is for reverse. if I test it using black as ground, then red for brake, and yellow for reverse and I hook them to the battery; black ground negative, red positive; then yellow positive one at a time and they light up, that would answer my question, Thanks

Donald T.

6/3/2020

@ChrisR the reason is the house is plastic, there is no place for it to ground other than the black. Thanks again

Kurt H.

7/12/2020

I have an old snowmobile trailer I am wiring and putting a new 4 pin harness on. The snowmobile trailer wires consist of a yellow, red, green, and black/brown wire. The 4 pin harness has white, green, brown, and yellow. What goes where? I assumed all colors went together and then red went with white but not the case. Please help.

Chris R.

7/16/2020

Going by colors alone isn't always the best method because trailer manufacturers and previous owners can get creative. My best advice for your particular setup will be to either trace each of the wires to see where they end up on the trailer or apply 12V power to them to see what functions they illuminate. From your new 4-pin harness the white wire is for ground, the green wire is for right turn/brake, the yellow wire is for left turn/brake, and the brown wire is for running lights.

Bob

11/16/2021

Can someone give me suggestions on how to hook up running lights on a trailer that is wired only with red and white wires?

Les D.

11/23/2021

@Bob Unfortunately, sometimes trailers get wired with any wire available. Occasionally you will see a trailer wired in one color only as that was the only wire on hand. You will have to use a tester like # PTW2992 to sort out the function of each wire.

Answer 1

This is a common question we get on lights like the LED Trailer Tail Light with License Bracket part #328-003-81LBM1. The original colors you have are the traditional trailer wiring code so brown=taillights, red=turn/brake and white is ground. On…

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Answer 2

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…

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Answer 3

Red, black, and white wires are common on many tail light assemblies. When this is the case, you will have red as stop and turn, black as running light, and white as ground. So you will connect yellow to red on one side of the trailer and green to…

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Answer 4

The black wire is for the running light circuit, and would be connected to the brown wire. The green wire would connect to the red wire on the lamp. On the drivers side, the black wire on the lamp would also connect to the brown wire for the running…

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Answer 5

A lot of trailer lights have 3 wires. One wire for running lights, one wire for turn signal and brake lights, and one wire for ground. Check the back of the light assemblies because it might indicate the functions of the wires. Other lights may only…

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Answer 6

Sounds like your converter has shorted out. However, since the running light circuit signal does not need to be converted it can potentially bypass a converter box. Most likely a short on the trailer's wiring is responsible for the box shorting…

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Answer 7

Hey Tom, that is odd that the running light circuit of the Curt trailer wiring part #C56400 isn't working but when converter boxes fail they oftentimes do things like this. For this circuit the converter box basically is just using the running…

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Answer 8

If your current brake assemblies are self-adjusting, once the hub/drum is removed you will be able to see the adjuster cable extending across the brake assembly as shown in the photo I have edited for you. If you find you do not have them, you can…

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Answer 9

The red wire is the turn signal wire and will be run to the green wire of your harness if its the right turn signal side, and the black wire will run to the brown wire of your harness. The yellow wire from your harness will run to the left turn…

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Answer 10

In regards to the 4-way wiring harness you are trying to install; the white wire is for the ground, the brown wire is for the running lights, the yellow wire is for the left turn/brake light, and the green wire is for the right turn/brake light.…

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Answer 11

Trailer axles are supposed to have a bow in them that faces down towards the ground. With the weight of the trailer normally this flattens out slightly and gives you the correct camber you need. Whoever flipped your axle should have used an over…

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Answer 12

The left side is the driver side, right side is passenger side. On a trailer brake assembly like #23-105 the arm that the magnet is on points to the front of the trailer and the magnet always will be on the bottom. I have included a picture that…

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Red, Black, and White Wire Functions on Old Trailer Light

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