Troubleshooting Trailer Lights and Dealing with Wiring Issues

Close up of a trailer's hitch with wires

We know how you feel - wiring issues can be frustrating. It’s always either hot or cold outside when there’s a problem. You look around for an adult to help you, then realize you’re the adult. Whether you are dealing with malfunctioning hydraulics or troubleshooting trailer lights, Affordable Trailers has dealt with it from plug to tail lights. We’ve seen it all. In fact, after 17 years in the business we’re going to publish here the world’s first definitive measure of stress vs. satisfaction levels when dealing with your trailer. (Then we’ll get to the helpful part).

Downsides to owning a trailerUpsides to owning a trailer
  1. Levels of Anxiety Over Potential Problems:
  • LEVEL 1 - 
    • Taking up two spaces in a parking lot
  • LEVEL 2 - 
    • Troubleshooting trailer lights
  • LEVEL 3 -
    • Watching your trailer pass you when you’re going downhill
    • Hurting someone in an accident
  1. Levels of Gratifaction:
  • LEVEL 1 - 
    • Taking up two spaces in a parking lot
    • Sporting a special license plate
  • LEVEL 2 - 
    • Flexing your dominance in front of trailer enthusiasts
    • Playing with a big toy but being able to call it work
    • Practicing the word NO in a mirror in case a relative asks to borrow the trailer or friends asks you to help them move
  • LEVEL 3 -
    • Getting to say, “Well, that’s not going anywhere,” as you strap down a load.
    • Hearing people cuss as they bang their shin into the trailer hitch
    • Showing off your finesse when backing up the trailer

As you can see, troubleshooting trailer lights is ranked pretty high as a potential stressor, just before a horrible accident, which is fitting since faulty lights may be the cause of the horrible accident. It goes without saying that no one wants to be reckless. In fact, trailer owners are usually some of the more skilled and careful drivers out there. So, what can be done to troubleshoot through your wiring issue? 

  1. Check out the easy stuff first. Are all the lights out or just one or two? Could be bulbs. Make sure the vehicle power is on and the connectors are together. Confirm that all the fuses are working. If any fuse repeatedly blows, the load may be too high and LED lights may fix that.
  2. The most common problem with wiring issues is not that actual wire. It’s the ground wires making bad connections. Be sure the ground wire is grounded to the trailer frame and not the hitch. Grounding to the hitch can cause flickering. The most likely cause of the bad grounding is corroded terminals or wires in the connector. Take some sandpaper or other abrasive material and clean up the connection. Electrical contact cleaner is a product that does a great job as well. You might consider replacing your crimp only terminals with Crimp and Solder Seal Terminals. They last longer, reduce moisture and contaminants, and keep a stronger connection. It can also be good to use dielectric grease on any of the system contacts. 
  3. If none of that has worked and you still want to fix it yourself, get a continuity tester and a tow vehicle tester. These will let you test the circuit, pinpointing where the problem is. When you have the plug disconnected, you can test each wire and terminal with your testers.Take a jumper wire, put one end in the connector and then put your continuity tester on the other end of the wire. If a tester is showing only one wire being bad and the connection is solid, then consider the wire. Through rubbing, pinching, and just old age, wires can break or corrode. Wiring kits are cheap and readily available. 
  4. At this point, we recommend bringing the trailer in for service. Some of the other problems include:
  • Lights won’t turn off. Insufficient ground connection, or you have a 4-way plug paired with LED lights. 
  • Lights quit working when the headlights are on. Could be an overload at the harness, or insufficient ground connection. 
  • Both turn signals work at the same time. Insufficient ground, likely at the harness. Look for the brake wire. You may have to look up which color it is based on which system you have. 
  • Connecting the trailer causes the harness to not work correctly. You guessed it...insufficient ground or overload. 
  • One light is not working and the bulb is fine. Could be several things: insufficient ground, weak connection, or blown fuse.
  • Others. Just come in. 

Well, there they are, the basics of troubleshooting trailer lights. Hopefully, keeping you moving safely will reduce your odds of getting to LEVEL 3 on the “Levels of Anxiety Over Potential Problems” list. With the curve ball problems or just the simplest of issues, contact Affordable Trailers. We’re eager to help you get the most joy and use out of your trailer as possible, while starting a relationship with you and offering you our excellent service. Contact us!

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1519 Old Hwy 17 N
North Myrtle Beach SC 29582


Office: 843-399-8654
Cell: 843-516-4586