Troubleshooting Running Lights Not Working On Trailer But Brake Lights And Turn Signals Work  

Question:

Expert Reply:

Since just the running lights on your trailer are not working, I recommend checking the owner's manual of your tow vehicle to find the fuse for the trailer running lights and make sure it is not blown.

If the fuse is OK then using a circuit tester like # PTW2993 with the head lights of your tow vehicle on check the 11 o'clock pin if you have a 7-way connector, or the connector right next to the exposed ground pin on a 4-way connector. If you do not have power to either of these pins, then there is a damaged or loose wire on the vehicle that you will need to track down.

If you have power to the vehicle connector, I recommend checking that the connector on your trailer is in good shape with no corrosion that could be causing power to not be sent to the trailer.

It is a good idea to go ahead and check the ground wires from your running lights, and the main ground on the trailer as a loose/bad ground can cause all kinds of issues and usually is most noticeable when multiple lights are on.

Lastly if the grounds are all tight use the # 40376 to check the running light wires on your trailer with the trailer connected to your tow vehicle and the vehicle head lights on. If there is no power to the light, there is a damaged wire between the trailer connector and running lights that will need to be replaced. If power is getting to the running lights but the lights are not coming on you will need to replace the light bulb, or the taillight if the bulb is not replaceable.

I included a link to a helpful article on wiring for you to take a look at.

expert reply by: Samuel C

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7-way Connector Wiring Diagram
(click to enlarge)

4-way Connector Wiring Diagram
(click to enlarge)