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Signal and Brake Lights Work on Trailer but No Taillights


Hi I hook the wire connector to my truck and my signal and brakes works but my tail lights dont work.I have 4 wire connector can u help on this.


Expert Reply:

Since the signal and brake lights are working but the taillights are not, it sounds like you may be experiencing a ground issue. A weak ground can be just strong enough to provide some of the lighting functions but not all of them. If a ground problem exists, it will typically show up when the taillights and brake lights are used at the same time because this creates the maximum amp load.

There are several places to look for a poor ground connection. I recommend starting with the trailer connector on the trailer. Check to make sure that the ground wire is secured to a clean metal surface on the trailer. In addition, each lamp/signal will also need to be grounded. Typically the lamp/signal is grounded through the mounting bolts having direct contact with the trailer frame.

If the area that the lights are mounted to is not a good source of ground, you will need to run a separate wire from each light to a clean, corrosion free, metal surface of the trailer to obtain your ground. This extra wire should be attached to the mounting bolt or screw that is connected to the lights internal grounding tab.

Next, I would take a look at the connector on the vehicle. You will want to check to make sure that it is free of dirt and corrosion and that this ground wire is also secured to a clean metal surface on either the vehicle frame or chassis.

If you find that all of the grounds check out to be fine and the lights on your trailer still aren't functioning properly, please feel free to email me and I would be happy to provide you with additional suggestions to try and locate the issue.

I have also attached a help article which covers ground issues that you may want to take a look at.

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