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Troubleshooting Trailer Wiring Harness on 2007 Dodge Magnum with Always-On Left Brake Light

Question:

I believe I recently purchased a trailer wiring harness for my Dodge Magnum from you. I cant find my receipt but I do have a record of the purchase on my bank summary. My problem is everything worked fine until today. This afternoon I noticed that my left trailer brake light is on all the time. I did some trouble shooting and out of the trailer receptacle on my car the left brake light is hot. Have you ever had this complaint before or do you know what the problem may be. Any help will be greatly appreciated. Thanks

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Expert Reply:

You did indeed purchase a trailer hitch from etrailer back in January of this year but I did not find a record of a wiring harness purchase.

In any case the problem you describe is most likely caused by either a damaged wiring harness or by a bad connector at the vehicle or trailer. I suggest you first check that the ground wire is firmly attached to a clean bare metal surface. A bad ground can cause all sorts of weird issues. If this does not help next disconnect the harness connectors from the vehicle tail lights, re-connect the taillight wiring as it was originally installed and make sure that everything works correctly on the vehicle. If not there is an issue within the vehicle wiring. You can also check for any bent or damaged pins on the vehicle and harness connectors.

With the harness re-installed you can also test the vehicle's trailer connector using a tester like # 40376 to see if the correct signals are present on the vehicle side. Please refer to the linked video.

If you have a 7-way RV-style connector (as shown in the linked photo) then you may have corrosion within it that has caused two circuits to become bridged together. For example, if corrosion inside the socket has caused the 12V power circuit and the left brake light circuit to become bridged, that would allow 12V power to continuously reach the left brake light. This would explain why it is always on.

Please see the two linked articles with troubleshooting help and let me know the results of your testing for additional help.

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