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Trailer Wiring and Lighting: Troubleshooting and Maintenance

One thing you need to check every time before using your trailer is the lighting and trailer wiring. Remember No lights, no brakes, no go! Here are some tips on what to check, and how to troubleshoot your trailer’s wiring and lighting if you do have an issue.

Before each Tow:

  • installed brake controller for trailers wiring lightingCheck that the electric brakes work by operating the brake controller inside the tow vehicle. Having your tow vehicle equipped with a brake controller is necessary for a trailer larger than 3000 lbs.
  • Check that all lights and turn signals work.  With the tow vehicle running and lights turned on, have someone stand at the rear of the trailer to watch the lights. Start with Turn Signals (left/right), Brake lights, and then Hazard lights.

“90% of all wiring issues are in the front plug, corrosion or broken wire.”
– Scott Brown, Felling Trailers’ Warranty Coordinator

Your Trailer: Wiring and Lighting

If the electric brakes, lights, or turn signals, do not function properly, start by making sure that the fuses in the tow vehicle are good. Check your owner’s manual to determine if your truck has fuses for the trailer circuits and that these are also good.

Sometimes the truck does not match the trailer wiring on a larger trailer like a deck-over tag trailer equipped with air brake. In this case, the running lights are on two different circuits. So if you have running lights but no tail-lights and license plate light, you can take the plug apart and hook the black with the brown wire. This can be a very common issue.

trailer wiring lighting testerFor troubleshooting, you will need a 12-volt test light. The Wiring Diagram can also be found here.

With any wiring issue, you should check the power at the truck plug first, then just behind the trailer plug. Then follow the wiring back. Now on a Felling Trailer, you can disconnect each section of the harness (the twist lock). This allows you to work your way back to the rear of the trailer.

Remember this Rule: No lights, no brakes, no go!

An improper electrical connection between the tow vehicle and the trailer will result in inoperable lights and electric brakes and can lead to a collision.Wiring on Trailers

Now that you have found the issue but need the trailer parts to fix it, visit and order your parts for fast delivery. If you prefer to talk to a Service Rep to make sure you have the right items on order, go ahead and give us a call at 1-866-335-5464.

If after checking your truck and trailer over, you are still unable to find the issue, call the Felling Parts and Service Department to schedule service at 1-866-335-5464 or email [email protected]. We are here to help!

More Articles you may be Interested in:
Tire Maintenance and Avoiding Tire Blowout
Trailer Inspection Checklist: Getting Ready for Spring


  1. problem with lights left side markers out Bu/t turns, break lights work, all side markers out left

    • Hello Randy, Here is the advise from our parts and service dept.
      “The markers (both left and right) should be supplied by the brown wire. I would use a test light starting at the plug and continue to the brown wire heading back, if you have only the marker lights on and pull the harness quick connect you can figure out which pin the brown wire is and then follow it back.
      I’ve attached a link which shows the color coding depending on plug and if you send me a vin I can send you a wiring diagram.

      Hope this helps
      Felling Trailers

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