Trailer Wiring: What to Check Before You Leave

Pull-behind trailers come in a variety of sizes, weight classes, and features. Whether you’re using a lightweight trailer to haul a few personal items, pulling a livestock trailer, a boat trailer, or a large equipment trailer; it’s important that the trailer has been wired correctly.

Imagine driving down the road at night when your trailer’s lights don’t work. Other drivers and pedestrians won’t know your vehicle has extended equipment on the back, which can lead to a dangerous situation. When others aren’t aware of your location, whether you’re turning or slowing down, your safety and the safety of others becomes compromised.

To be an aware and careful driver on the road, you need functioning trailer lights. (They’re crucial for safety.) Because everything wears out over time, it’s best to check your trailer light wiring every time before you drive.

Before Each Tow:

  • Check that the electric brakes work.

    Use the operating brake controller inside the tow vehicle to test the brakes.        Note: 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.

A Checklist for Trailer Lighting Issues:

Test for Proper Functions

  • Loose connectors or wires and missing fuses or relays on a plug-in harness
  • Weak or loose ground connections on a hand-wired harness
  • Wires that are attached to the incorrect places on the truck

Confirming Accurate Wire Connections

  • trailer wiring checkSecure the connection between the 12V power wire and vehicle battery while checking for blown fuses.
  • Confirm that the harness connectors are on the proper side of the vehicle, with green wires on the passenger side, and yellow on the drivers.
  • Make sure the connectors click together by removing and connecting them again.
  • Inspect the connectors for loose or damaged wires, loose or bent pins, and broken locking tabs.

Inspect Ground Connections

  • 90% of all wiring issues are in the front plug, corrosion, or a broken wire.
  • Be sure the ground on the tow vehicle is connected to an unpainted surface on the chassis.
  • Inspect all the wire runs along the trailer to be sure that it is supported frequently and protected from chafing against the trailer and abrasion from heavy road use.

After you’ve troubleshot the wiring system on your trailer, you may find that you need some extra support. For more advanced problems that you can’t fix on your own, bring your trailer to the Felling Trailers Service department.

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