Tail Lights not Functioning on Small Cargo Trailer  

Question:

Expert Reply:

The first step would be to determine if the problem lies within the vehicle wiring or the trailer wiring. Use a circuit tester such as part # PTW2993 and test your trailer connector. Test the pin for the running lights. This pin would correspond to the brown wire on the connector.
If you get power on this pin while the vehicles headlights are turned on, then the problem exists on the trailer. If there is no power on this pin, how you proceed will depend on your vehicle and how the trailer wiring harness was wired.
If your vehicle has the factory tow package, many times there are fuses which protect the tow lighting circuits. Check for a blown fuse, and replace if necessary. If your trailer wiring harness is directly wired into the taillight circuits of the vehicle, you will have to trace that brown wire back to its connection to the vehicle wiring. Look for a loose connection or a broken wire. If your vehicle uses a taillight converter, as you are tracing the wiring, you will come across a small black box. You can test the brown wire before it enters the box, and see if you are getting signal there (once again, as the headlights are on). If you get power on that circuit on the input side of the box, but not the output side, the box is bad and must be replaced.
If all on the vehicle checks out, you will have to trace the taillight circuit back from the connector on the trailer. Examine the connector itself, making sure its not damaged or corroded. As you follow the taillight circuit back, look for pinched wires and cracked or worn insulation on the wire. Any bare metal on the wire could allow the circuit to short out if it contacts the trailer frame.

expert reply by: Mike L

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