Tail Lights Go Dim or Out When Brakes are Applied

Question

Question:

I rewired my trailer and now have the following problem. Left and right blinkers work as do running lights, however when the brakes are applied on the vehicle the tail lights go out. This is small utility trailer connected with 4 pole flat plug to 2004 ford ranger with factory tow package.

asked by: Richard

0

Expert Reply:

It sounds like you have a bad ground connection. If all ground connections are not making good contact to bare metal, when the brake pedal is pressed and the tail lights are on, the increased amperage draw will make this problem show up.

You will need to check all of the ground connections especially where the taillights are mounted to the trailer frame, and where the light brackets are mounted if they are bolted to the frame. If a plastic license plate holder is mounted between the left side taillight and the trailer frame this could be the problem.

Once you have all of ground connections checked, if the problem persists, you will need to check for a broken pinched or frayed wire on the trailer somewhere. If this is not the case then you will need to use a circuit tester, item # PTW2993 if needed, and make sure your wire connections have been properly made at the taillights.

expert reply by: Robert G

0

Steven P.

9/7/2020

My 97 Tahoe when I hook up my trailer all the lights work fine until I turn on headlights then the trailer lights dim. Thanks,

Reply

Jon G.

9/9/2020

You will want to walk through the same troubleshooting steps that Bob mentions above for the running light problem. Here is a link to our wiring troubleshooting FAQ that you can check out.

Helpful Links

faq-4-5-way-troubleshooting.aspx

Reply

Answer 1

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…

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Answer 2

Most often the root cause for issues with trailer lighting is a weak ground. Strange as it may sound, a loose or rusty/corroded ground can cause a vehicle's trailer wiring harness to badly misbehave and shut down some functions. It may also…

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Answer 3

What you describe is a ground problem with the trailer wiring. Starting at the rear of the vehicle, confirm that the ground connection on the Plug and Tow Harness is securely fastened to bare metal. If there is undercoating, corrosion, or grime built…

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Answer 4

It sounds like you have a short somewhere. This is the result of a bad ground or some damaged wiring. Check your grounds and make sure they are secure and connected to clean, bare-metal surfaces and that your wiring isn't damaged or pinched. You…

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Answer 5

Your brake lights and turn signals for each side are on one circuit. The left side turn signal and brake light is generally the yellow wire going into your trailer connector. The first thing to do is check the fuses on your tow vehicle. Next, inspect…

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Answer 6

It sounds like there is a short somewhere along the wiring of your vehicle or trailer that is causing a fuse to blow every time you connect. The first thing I recommend doing is disconnecting the trailer and using a circuit tester like #PTW2993 to…

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Answer 7

The fuse on your 2000 Ford F-150 that is for the trailer right turn and stop lights is the number 19 fuse in the power distribution block in the engine compartment. If you check in your owner's manual on page 182 you can see the exact location in…

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Answer 8

There are a couple issues you may be having. You may have a bad ground or short on your trailer wiring and when you hit the brakes the short causes an excessive drain on your vehicle battery and your lights dim. If you see the voltmeter on your dash…

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Answer 9

Since you are not getting the 12V power when your truck is running, you most likely don't have a fuse issue as you stated their isn't a specified fuse or relay in the owners manual. The issue is that your truck is computerized even at the…

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Answer 10

When a tow vehicle is equipped with a bulb-out sensor, the addition of LED trailer lights can cause hyper flashing like you describe because LEDs draw much less power than incandescent bulbs do. This fools the bulb out sensor into thinking that a…

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Answer 11

It sounds like there is a short circuit that is overloading the running light circuit in the tow package wiring on your tow vehicle. The most likely culprit is a dirty or corroded trailer connector on the vehicle or trailer if not both. The first…

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Answer 12

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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Tail Lights Go Dim or Out When Brakes are Applied

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