Troubleshooting No Running Lights on Trailer  

Question:

Expert Reply:

There are a few common causes to just one function on the trailer not working such as the running lights in your case.

A good place to start any troubleshooting process like this one is to test the connector on your tow vehicle with a circuit tester like # PTW2979. Test the running lights pin on the connector with this function activated on the vehicle. If you get power at the pin then you know the issue is on the trailer. If you don't get any power there then the issue is actually on the vehicle.

If you didn't get power at the connector I recommend checking the vehicle's owner's manual to see if there is a trailer running lights fuse inside the power distribution center. If so, make sure this fuse is present and in good condition, replacing if needed. Then make sure the connector itself at the rear of the vehicle is free of any corrosion or debris that needs to be cleaned out.

If the fuse is good or you don't have one, the next thing to look at is the ground connections on the trailer. A weak ground can allow some of the functions to work on the trailer but don't allow enough power to the assemblies when higher current functions are activated (like the running lights). Make sure the main connector ground is attached to a clean, bare metal surface on the trailer. Also do the same for the trailer light assemblies themselves, whether they ground through their mounting hardware or through a dedicated wire.

If the issue persists please let me know and we can continue to troubleshoot.

expert reply by: Chris R

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