Troubleshooting Trailer Running Light Signals from 2015 Ram 2500  

Question:

Expert Reply:

Since you have changed out any blown fuses related to trailer lighting in your 2015 Ram 2500 I suggest you test the truck wiring without the trailer connected. This will help you isolate the problem to either the vehicle or trailer side.

Please refer to the linked photo (and article on trailer wiring) which shows the function carried on each pin of a 7-way vehicle socket. Running light power is carried on the 7-way contact at the 11-o-clock position as you look at the socket from the back of the truck.

Use a circuit tester like # PTW2993 to test the pin for a signal when the truck lights are on. If you do not detect a signal check for corrosion on or inside the socket. Also check the main wiring harness ground wire that attaches to the frame to ensure it is attached to a clean bare metal spot that is free of rust, undercoat, primer and paint. The ground must be made to clean bare metal in order to be able to pass all the power for the trailer lights.

You can also test the trailer directly, when it is not connected to the truck, by applying power directly from a well-charged battery (a spare or the one in the truck) to the ground and running light contacts on the trailer plug (again, please refer to the linked article). If the lights do not work even when fed this direct power then check the trailer's main ground just the way you did on the truck and also inspect its plug for any signs of internal corrosion within the plug housing. If a new 7-way plug is needed we offer them in several lengths, such as # H20046 which is 8-feet long.

expert reply by: Adam R

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