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Trailer Lights Not Working? Try These Troubleshooting Tricks

If your trailer lights are not working, diagnosing the problem and getting them up and running can be frustrating. Unfortunately, many drivers experience issues with these critical safety components. This can be very dangerous for you and others on the road.

Luckily, there are some troubleshooting tricks that you can use to pinpoint problems. We have diagnosed and repaired many trailer lights over the years and you can too! If you have the correct tools and some DIY skills, you and your trailer will be back on the road in no time.

Today, we’ll explore some common reasons trailer lights are not working and solutions for fixing them. Let’s get started!

What Are Trailer Lights?

Trailer lights are crucial safety features that increase your trailer’s visibility. They consist of a set of lights on the trailer that help signal to other drivers on the road the presence and movement of the trailer. They typically receive their power from the tow vehicle’s electrical system.

For a safe towing experience, these bulbs must be in proper working order. You must check and maintain them regularly. This reduces the risk of accidents or legal issues from a faulty or malfunctioning system.

Close up of travel trailer lights
Your trailer lights are critical safety components to your rig you must take care of.

Are There Fuses for Trailer Lights?

Most of the time there are no fuses for trailer lights on the trailer. The power comes from the vehicle and you will find the fuese in the vehicles wiring. Find the tow vehicles fusebox and look for fuses designating trailer.

However, not all vehicles have dedicated trailer light wiring. Many times aftermarket trailer hitch installations utilize the existing vehicle lighting circuits for power. This means that the wires are tapped directly into the lights for the stop, running and turn lights of the vehicle. In this case the fuses would be the same ones for the vehicle lights.

While a fuse is not a bad place to look for problems, they generally are not the cause of trailer lights not working.

Pro Tip: We shone a light on Everything You Need to Know About RV Lights.

How to Test the Trailer Lights

You should always do a pre-trip inspection before hitting the road. One step of this inspection should include thoroughly testing the trailer’s lights to ensure they’re working. Unfortunately, having a second set of eyes is the easiest way. However, it’s not impossible to do it solo if you have no choice.

If you’re lucky enough to have a companion, one person can walk to the rear of the trailer while the other stays behind the wheel of the tow vehicle. You’ll want to press the brakes, use turn signals, and turn on your running lights. You can use cell phones or walkie-talkies to make it easier to communicate.

Alternativly you can use your cell phone to do this test if you’re by yourself. All you’ll need to do is find a spot to set your phone so the camera points at the rear of your trailer. You can then record a video while you perform the same test. Afterward, you can review the video to ensure all devices operate correctly.

Close up of trailer lights
Use some troubleshooting tricks to pinpoint what problems may be causing your trailer lights to not work.

Troubleshooting Tricks to Diagnose Trailer Light Issues

Diagnosing trailer light issues can be challenging. Unfortunately, they won’t likely fix themselves, and you can’t afford to ignore them or procrastinate. We’ve learned a few tricks that have helped us troubleshoot issues quickly and effectively. 

There are three places problems can live. On the trailer side, the wiring connections, or the vehicle side. Lets take a look at all three.

Check the Wiring Connections

One of the most common problems for trailer light issues is problems at the connections. Because trailers disconnect they have plugs that connect the vehicle and trailer. Loose or corroded connections can cause the trailer lights to malfunction or stop working altogether. Inspect the wiring harness connections between the trailer and the tow vehicle. You can wiggle the connection and have someone watch the lights to see if they flash on and off. If they do the connection needs cleaning.

It’s common for gunk and other debris to get inside these connections. As a result, you’ll need to clean them out from time to time. You can use a wire brush or sandpaper to clean and remove corrosion. Using an electrical contact cleaner can prevent future build-up or issues.

In addition, there’s a chance that something has damaged the wiring connections. Inspect the wiring and look for any signs of damage to the tow vehicle’s wiring. You may need to replace any damaged components to fix the issue.

Pro Tip: Learning the ins and outs of how RVs are wired can be complicated. Check out this Helpful RV Electrical Basics for Beginners to make the learning process easier.

trailer wiring plug
The trailer plug is one of the most common problem areas. Make sure they are clean and free of corrosion.

Vehicle Side Check

The tow vehicle is where the power originates for trailer lights. Let’s examine some of the most common problems you should check on the vehicle side of the towing setup.

Check the Fuses

Like mentioned before the fuses might be specific for trailer lights, or the same ones as the vehicle lights. Regradless checking the fuses is one of the easist first steps in looking for trailer light problems.

Test the Trailer Plug

A trailer connection tester is a handy diagnostic tool for these situations. You can instantly plug it into your trailer’s power cable and diagnose issues. Just ensure that you get a connection tester that’s compatible with your trailer’s wiring connections.

CXTM 7-Way Trailer Plug Tester, 7 Way Trailer Plug...
  • EASY INSTALLATION & DISASSEMBLY: Simple plug-and-play design,...
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  • MULTIPURPOSE USE: This 7 pin trailer plug tester tests for...

Alternativly you can use a multimeter to check for voltage on the correct pins. Set the unit for V or voltage. You will also need the trailer plug pinout configuration so do a search for your specific plug type. Then with the vehicle on check for voltage between all the pins that should be on (brake when pressing brakes, running when headlights are on, and turn signals blinking power when on and off. If you are not getting a reading then its possible there is a problem in the wiring.

Check for Physical Damage

If you’re having electrical issues with your trailer, you’ll want to look around for any signs of physical damage. Rocks and debris on the road can hit wiring and components while hauling your trailer down the highway. Routine inspections make it easier to spot potential issues.

If your trailer is in storage, you must thoroughly inspect it for physical damage. Mice and other critters love making meals from almost anything, including wiring. The sooner you check for damage, the sooner you can address the issue and avoid potential delays.

Trailer driving through forest at night with trailer lights
Your tow vehicle can also be causing your trailer lights to not shine as they should.

Trailer Side Check

There’s a chance that the issue could be on the trailer side of the connection. Here are some things you should check on the trailer to narrow down the possibilities.

Check the Bulbs

While it may not be the first thing we’d check when the lights are not working on your trailer, you can’t overlook the possibility that a bulb could be faulty. This could be your issue if it’s been a few years or you’ve never replaced the bulb. If you’re only having problems with a single bulb, it’s worth a shot to quickly drop in a new one and see if that fixes the issue.

Check for Physical Damage

Loose connections, broken wires, and corrosion can wreak havoc on your trailer’s electrical system. It would help if you regularly inspected the connections and wiring. It’s best to discover issues beforehand to fix them before they become more challenging problems.

If you want to limit corrosion, consider how you’re storing your wiring and other connections. We recommend finding a way to cover them as often as possible to keep the sun, rain, and different weather off them.

Check for Shorts

If the bulbs and wires seem ok then its time to dig into the electrical side. For this you will need a multimeter. You will also need to identify the pins on your trailers plug. There are many plug types but the most common are the 4 pin and 5 pin flat or 7 pin round plugs. Do a search online for your plug style or “trailer plug pinout

Set your multimeter to ohms or continuity where it beeps or reads 0 or OL when you touch the probes together. Now locate the ground pin and touch one of the multimeter probes to it. Take the second one and touch bare metal on the trailers frame. The unit should read 0 or OL as if the two leads are touching. If you don’t get a reading then the ground wire is not grounded to the frame properly. You will need to find where the wire connects to the frame and fix it.

Next take the probes in the same mode and touch each of the other lighting circuits and the ground pin. The meter should read something but not 0. If the meter reads 0 then there is a short in that wire to the trailer frame or ground wire. Shorts are a common cause for lights to fail or fuses to blow.

Alternativly you could buy a trailer light tester unit

trailer light plug
You can use a multimeter to check that the ground (left most connection) is not shorting to the other wires.

When to Seek Professional Help

If you’ve tried all the tips and tricks we’ve shared and your issues persist, you must call a professional. They’ll likely narrow down the problems and fix them for you. You should never hit the road hauling a trailer that you know is having electrical issues. Look for mobile mechanics that can come to you and fix your trailer on the spot.

Common Reason for Shorting Trailer Brakes - Electric Trailer Brakes - Check Your Axle Wires

Get Your Trailer Lights Working Again

Trailer light issues can be frustrating and dangerous, and taking the necessary steps to get them working again is vital. We’ve shared some tips and tricks for troubleshooting and diagnosing common issues. However, if you continue to experience problems or are not confident in your ability to fix them, it’s best to seek professional help to avoid any potential accidents on the road. The most crucial thing is to keep you and others on the road as safe as possible.

Do you carry spare fuses for your trailer? Tell us in the comments!

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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