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Fixing Common Trailer Light Issues

Trailer Light Issues

We rely on our trailers whether you use it for landscaping, construction, farming, racing or any number of other hobbies or work. Hauling things like heavy equipment, tools, motorcycles or anything else you might put in or on your trailer requires your trailer to be not only durable, but also safe.

If your trailer is begining to show its age, there is a good chance that you have had, or will have issues with your lights. Trailer lights are crucial for trailer safety so please check your lights every time you use your trailer. Some things like a burned-out bulb or a bad ground wire, can be pretty simple to repair while other things can be a real challenge to diagnose and correct. Here are a few pointers to help you keep your trailer lights working properly.


What Tools and Materials do You Need?

The most helpful tool to use will be a 12V probe-style circuit tester. In addition, you will want to have basic wiring tools on hand. These include electrical tape for repairing connections, a wire stripper for cleaning up wire ends, dielectric grease, and various wiring fasteners like butt connectors, quick splice connectors, or ring terminals, depending on the type of repairs required. Wiring kits that include these items are available.


  • 12V Continuity Tester
  • Wire Cutters/Strippers
  • Electrical Tape
  • Various Electrical Connectors
  • 220-Grit Sandpaper & 3/8” Wooden Dowel
  • Electrical Contact Cleaner
  • Replacement Bulb
  • Wiring Kit or Additional Wire
  • Basic hand Tools (Screwdriver, Pliers, Etc.)
  • 12V Battery or a Tow Vehicle


Where to Begin

Check your vehicle's plug configuration. Hook up your trailer and connect the trailer light harness. Have a helper stand back to see if the running lights, stoplights and blinkers are working properly. If all the lights appear dim or you have no lights at all, check the trailer light harness at the tow vehicle. First disconnect the harness and plug a tester into the receptacle from your vehicle. Your 12V tester will tell you immediately if you have a problem in the trailer light wiring from your car or truck. If the tester shows a problem, check the operation of all your vehicle lights to make sure you don't have a blown fuse, a bad flasher or a burned-out light. Clean the connector and check again. You will also want to check for broken or exposed wires near the connector.


Testing Your Lighting

For a hard wire installation, confirm that each wire is connected to the right location. There are traditionally standard wire colors, but make sure to check connections according to their functions on your specific system. If your vehicle has combined brake lights and turn signals, your brake wire will be grounded with the color white. A 12V power wire should connect to your car’s positive battery terminal, and if your trailer has a 5-way harness wire, be sure the vehicle’s 5th wire connects to the reverse light circuit.

When it comes to your plug-in installation here are a few things you can inspect:

  • Secure 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 driver’s.
  • 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.

You may also need to perform a continuity test to troubleshoot your trailer wiring. Connect a jumper wire to the connector pins and the continuity tester to the system’s sockets. A continuity test helps you see if there are any broken wires. Select a color of wire in the socket and find the same one on the connector front. Clip one end of the jumper wire to the connector pin and clip the other to the continuity tester.

Probe the tester inside the socket. If your trailer lights are failing, trace the wire and check for breaks. Cut anywhere you see a fault, then solder on a new connection, and repair the insulation with heat-shrink tubing.


Check Your Connections

Clean the ground contact and tighten the ground wire to the metal frame. Next, check the ground wire. Many problems occur here. Remove the ground screw and sand the wire terminal and trailer chassis contact with sandpaper. If the ground screw itself is corroded it should be replaced.

Remove corrosion with fine sandpaper and 3/8-in. dowel to get into tight spaces. If the light still doesn't work, you may have corrosion in the socket at the contact points for the bulb. Attach a bit of 220-grit sandpaper to the butt end of a 3/8-in.dowel. Clean the contact points by spinning the dowel and moving it side to side. Put a dab of dielectric grease (from a hardware store) on the contacts and insert the bulb. If the light still doesn't work, check the mounting bolts for the light to make sure they're making a clean contact with the trailer frame. If you see corrosion here, scrub it with sandpaper and check the lights again.


Other Possible Issues

An overloaded circuit happens when a circuit is transmitting more electricity than it can handle. An overloaded circuit can cause over heating and even melting. You should always check the maximum amperage rating of your harness and be sure that your lights (or other accessories) are not drawing more than the circuit can handle. If you are experiencing an overload on a circuit you may be able to replace running lights with an LED version to reduce the draw.

Over time most trailers are going to experience corrosion from the elements. You should check your trailers electrical connections and clean or replace any that are corroded. You can spray the connection with electrical contact cleaner or even use sandpaper to clean the connection and create a stronger connection.

if your trailer is still experiencing electrical or light issues you can always rely on the professionals at USA Trailer to help. We can correct any wiring or light issues and even re-wire the entire trailer if needed.

Experts You Can Trust

The experts at USA Trailer Sales carry a huge selection of hitches, trailers and accessories. We are always here to help you negotiate the many options and possible customizations available when buying your trailer. Please contact us with any questions you may have or stop by one of our six Michigan locations to speak with a local trailer expert today.