Why Are Trailer Running Lights Coming on When Brakes are Applied

Question

Question:

Trailer 5th wheel clearance lights come on when brakes applied. As title suggests my clearance lights come on when braking, this all happened after installing a 4 point plug at rear ,now all lights work correctly on the secondary trailer . I also tried the trailer on another truck and same problem so that rules out my truck. Where did I go wrong ,all 5th wheel trailer lights work correctly.

asked by: Herman M

1

Helpful Expert Reply:

You are correct that the issue is on your trailer and based on what you are describing the circuits are somehow swapped when you installed your connector; unfortunately, I was unable to find your order number to see what you purchased from us for the install that may have caused this to happen. It is also possible that the brake and running light circuits shorted out and surged together. Either way, you will need to trace your wiring back, particularly at the running lights to see where any wires are crimped, broken or otherwise damaged. I have also added a link to a help article on wiring troubleshooting which I highly recommend reading.

expert reply by: Kyle S

1

Answer 1

Your problem is in the wiring in one of two places. It is either on the vehicle wiring harness or somewhere in the wiring on the trailer. The first thing to do would be to narrow it down to one of these two places, then we can pin-point the problem…

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Answer 2

You can use both the RoadActive Suspension Enhancement Kit #RAS4611 and the Timbren Suspension Enhancement Kit #TGMRCK25D at the same time. The Roadmaster kit will take care of the travel the initial travel of your suspension, the Timbren will just…

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Answer 3

If you check out the picture I attached the middle set of 7-ways is the wiring diagram/colors you'll need to use for the Ford Replacement OEM Tow Package Wiring Harness #118243 that you referenced. The harness is already wired up correctly though…

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Answer 4

What you are describing is normally the result one 1 of 3 issues: First, there could be some corrosion in or on the connectors on the vehicle or trailer side or both. Second there could be a bad ground. Bad grounds can cause all sorts of bizarre…

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Answer 5

I know you said you checked the fuses, but on your 1999 Ford F-250, the Power Distribution Box and Trailer Tow Relay Blocks are located in the engine compartment near the brake master cylinder, not to be confused with the Fuse Panel located below and…

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Answer 6

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 7

To check the pins on the vehicle side 7-Way, you can use a circuit tester or the volt meter. The circuit tester will show you if a signal is coming through on the pin you are testing while the volt meter will tell you that and how much voltage is…

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Answer 8

The most likely cause for the incorrect behavior of your trailer lights, where activating one turn signal causes all trailer lights to blink, is an insufficient ground (or a short to ground) on either the vehicle or the trailer. Since you re-wired…

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Answer 9

The lid of the Bright Way Trailer Breakaway ICU Kit with 12V, 5-Amp-Hour Battery, Charger, and Wire Loom #BW94FR that you referenced has a wiring diagram shown that details how it wires. Not seen is there is a single wire that runs up to running…

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Answer 10

It sounds like you have a ground issue. When trailer lighting does not have a sufficient ground many different scenarios can show up, but the most prevalent is when the most amperage is applied, like tail lights on and brake pedal pressed, the lights…

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Answer 11

We know from Tekonsha training on their universal-fit ZCI Circuit Protected Vehicle Wiring Harness #119250KIT that this item is very sensitive to the initial setup process, which must be followed exactly for correct operation. My technical contact at…

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Answer 12

I checked and Curt hitch #C13117 is listed for all models of the 2013 Mercedes ML350 as long as it does NOT have the Active Curve System which is a hydraulically activated anti-sway/roll bar. Installation is rank a 5 out of 10. I have linked the…

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Why Are Trailer Running Lights Coming on When Brakes are Applied

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