Troubleshooting Trailer Running Light Circuit Seemingly Not Active on Truck
Question:
Need help with trailer lights. All turn signals and break lights work but no running lights. What fuse do I need to check for running.
asked by: Carlos S
Expert Reply:
There should be a fuse under the hood of your vehicle that would be labelled trailer running light circuit that you'd need to check, but typically this issue corrosion on the pins of the trailer wiring connector preventing contact.
First thing you should do at this point is test the pins of the wiring harness with a circuit tester like # PTW2993 for voltage on all of the right pins when the taillight signals are being applied. Just like in the video I attached.
If the voltage checks out there but the trailer lights still don't function right then the problem is on the trailer wiring. That would mean that problem is either due to a ground issue or a short issue.
Make sure that the trailer side connector are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.
If the problem is on the vehicle side then I would first recommend you double check how the harness is installed on your vehicle, make sure all of the connections are good and tight. You should check all towing related fuses and relays as well.
Products Referenced in This Question
Product Page this Question was Asked From
Continue Researching
- Article: Trailer Wiring Diagrams
- Q&A: Trailer Running Lights Do Not Work but Brake Lights and Turn Signals Do Work
- Article: How to Troubleshoot Your RV Air Conditioner
- Article: Brake Controller 7- and 4-Way Installation Kit (ETBC7)
- Article: Brake Controller Installation: Starting from Scratch
- Article: Testing Trailer Brake Magnets for Proper Function
- Q&A: How to Test Brake Controller without Trailer Connected
- Article: Troubleshooting 4 and 5-Way Wiring Installations
- Q&A: How to Make an Adapter to Go from Semi Truck 7-Way Round to RV Style 7-Way Blade on Trailer
- Article: Wiring Trailer Lights with a 7-Way Plug (It's Easier Than You Think)
- Q&A: Trailer Turn Signals Both Blink when Just Left Turn Signal is Activated
- Q&A: Troubleshooting No Running Lights on Trailer but Turn Signals and Brake Lights Work
- Q&A: Will The Curt Dinghy Wire Harness # C96JR Interfere With Activation Of A Blue Ox Patriot
- Q&A: Checking Trailer Lights Without Hooking Up to Vehicle?