Trailer tail lights not working? Here’s a simple trick to try when troubleshooting why trailer tail lights are not working, while the other lights do. tl;dr Clean the trailer plug and socket connectors.
We discovered the tail lights on our trailer were not lighting up with the headlights turned on. Yes, the trailer cord was connected. Only the reverse lights on the trailer and the tail lights were not working. The trailer blinkers and brake lights were both working. So, I dove into this mystery to track down the gremlins causing this issue.
Troubleshooting Trailer Tail Lights Not Working
Connect your trailer and turn on your headlights. Do the tail lights and running lights on your trailer light up? If so, fantastic. No need to read any further. For trailer tail lights not working, try these simple steps first.
Check the trailer light bulbs. If all trailer running lights are out, and the tail lights do not light up, the issue is probably not bad bulbs. To rule out the simplest solution, however, check the trailer tail light bulbs and replace if they appear burnt out.
Next, ensure that your trailer cord is seated firmly in the socket. Then, take a close look at the connectors inside both the plug and socket.
Corrosion, debris, and oxidation can all prevent clean contact between the plug and socket connection. For best results, use a small needle file set to clean all the the connection points inside the trailer plug.
You will need a small steel needle file to clean the connectors. Use the tip of a flat needle file to remove any corrosion and oxidation. Blow into each connection to remove any dust and filings. (TIP: Close your eyes before blowing!)
Thoroughly clean each connector in the trailer cord plug. Do the same for each of the terminals inside the socket.
Ensure there is firm contact between the socket terminals and trailer plug connectors. You can gently bend the center connector and/or leads inside the socket to create more contact point pressure. Be sure to bend the blades outward to create better contact with the leads on the outer circumference of the plug. (Disclaimer: Your plug may differ.) Don’t bend them too far, or you my not be able to seat the plug into the socket without bending them back.
NOTE: Be careful not to touch the power lead in the socket to any other connector!
Refer to this 7-pin RV plug and outlet wiring diagram for reference. This will tell you which contacts may cause the trailer tail lights not working problem.
Once you have cleaned all the contact points in the plug and outlet, reconnect your trailer. Turn on your headlights, and check to see if this fixed the trailer tail lights not working.
This worked for me! Unfortunately, my reverse lights were still not working on the trailer. My next steps will be to replace the plug and outlet. Thankfully, I have done this before and have detailed instructions in these previous posts: