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Troubleshooting 4-Way Wiring Harness Brake Lights Work But Running Lights Do Not Work

Question:

Does the running light wire and brake light wire work off the same wire on a 4 pin flat trailer connector? My brake light comes on but the running light does not

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Expert Reply:

The color code for wiring harnesses can vary between manufacturers, but the general standard for 4-way plugs is as follows:

Green: Right turn/brake light
Yellow: Left turn/brake light
Brown: Tail/running lights
White: Ground wire

The running lights are on a different wire so they are not tied to the brake lights or turn signals. Since one function is not working I recommend checking your ground connection. Make sure it is secure on a clean, bare-metal surface. You can also try unplugging the 4-way and plugging it back in to make sure the connection is seated properly.

If you still have a problem I recommend checking the connection on the vehicle using a circuit tester like the # PTW2993. If the vehicle side checks out then you need to check the wiring on the trailer for a short. If it does not, then I would check for a short on the vehicle side wiring.

I have attached some helpful articles on 4-way wiring for your reference.

expert reply by:
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Robin H

Question:

Question. i have an 02 Dodge Ram 1500. My 4 pin flat connecter on vehicle for trailer works fine. EXCEPT THE RUNNING LIGHT. My 7 pin connector on vehicle for trailer works fine. EXCEPT THE RUNNING LIGHT. What do you recommend? Thanks.

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Expert Reply:

I'm not sure what you have tried since my previous suggestions but with one function not working I would still say the first thing to check would be your ground. I also do not know what your exact setup is for the wiring harness but the 4-way and 7-way are going to be running off of the same wire.

Since the same function is having an issue on both, you should be checking that wire for a short. If you are unable to locate the problem I recommend taking your truck to a local shop to take a look and see if they can figure out what is wrong with the wiring.

expert reply by:
0
Robin H

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