Troubleshooting Trailer Running Light Circuit that Turns Off When Interior Lights are Turned On

Question

Question:

Why do my running lights go out when I turn on my interior lights on trailer. I have two interior stock lights inside trailer if I just turn one on it’s fine when I turn them both on the running lights go out on trailer and it doesn’t matter what one I turn on first?

asked by: Dean S

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Expert Reply:

Your problem is due to your trailer wiring ground circuit being insufficient. Basically you are trying to draw more amperage than you ground circuit is capable of keeping up with so it's shutting down partially. Since the interior lights and running lights are on separate circuit it wouldn't be an overdrawing of either circuit so it's definitely a weak ground.

So you need to improve the ground of the trailer wiring. You can do this by running jumper wires from the circuits back to the main ground harness. Improving the connection of the main ground harness to the trailer frame or making sure that all of the circuits that ground through their hardware are connected to a clean metal surface.

I attached a help article on trailer wiring troubleshooting for you to check out as well.

expert reply by: Jameson C

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Answer 1

Sounds like you have a ground issue on your trailer. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light but can show up any…

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Answer 2

You do have the wishbone trailer wiring setup. What that means is that if you have a solid brown wire it attaches to the brown and green wire as well as the brown and yellow wire. Yellow goes to left stop/turn, green goes to right stop/turn, and…

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Answer 3

A 4-Way trailer connector has the basic lighting functions only; running lights, left turn signal and brake lights, right turn signal and brake lights, and ground. A 7-Way has these functions and a 12 volt circuit, a circuit for electric trailer…

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Answer 4

Lance does have a proprietary plug, but many customers see a standard 6-way or 7-way round and notice it doesn't fit their factory 7-way as well. I've attached an article to help if you have one of the 7-way or 6-way round connectors which we…

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Answer 5

When wiring a trailer connector, it is best to wire by function, as wire colors can vary. We have an excellent wiring diagram on our website, I will provide you a link so you can look at it. If you are looking at the inside of the trailer connector…

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Answer 6

If your trailer has 7 wires running all the way back to the brakes, then yes, you can tap into the existing wiring. Each of your new brakes will have two wires for the brake magnet. One wire is for 12 volt power to the brake magnets and the other…

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Answer 7

Since wire color codes are NOT universal, we always recommend wiring by function, rather than wire color. If you look at the Trailer Wiring FAQ article I have linked you to, you can see some diagrams showing the proper way to wire a vehicle and…

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Answer 8

The difference between the Class II and Class III hitches has to do with their Gross Trailer Weight (GTW), their Tongue Weight (TW), and their Hitch Receiver Size. Class II trailer hitch receivers have a 1-1/4 inch receiver and can be rated up to…

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Answer 9

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 10

It could be a tow package fuse on the vehicle. Use the owners manual to find the locations of fuses/relays related to the tow package wiring to check them and replace as needed. If the issue is not a fuse or relay then you can test the vehicle side…

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Answer 11

The only difference between 7-Way Utility and 7-Way RV is the color of the wires. The pin outs are the exact same so either would work just fine with the other. If you check out the picture I attached you'll see that the functions are all the…

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Answer 12

Your 4-pin/5-wire wiring harness is what is called a "wishbone" type which simply means that there are two separate running light wires, one brown and one pink. This allows a separate running light wire for each side of the trailer which…

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