Left Turn Signal And Brake Light Not Working On Trailer (Solved!)
Are you having an issue with the left turn signal and brake light not working on your trailer? If yes, you’re not alone. Many other trailer owners have dealt with this issue at some point. In this guide, we’ll educate you on why this happens and the steps you can take to resolve it.
The left turn signal and brake light not working on your trailer can be caused by a variety of issues such as bad bulbs, wiring issues, blown fuse, faulty connectors, and even poor ground connections.
In this article, we’ll share more helpful insights on the potential causes behind this problem. Moreover, you’ll discover our step-by-step guide for troubleshooting and resolving this frustrating issue. By the time you’re done reading this article, you’d have your left brake light and turn signal running flawlessly again.
Why is your left turn signal and brake light not working on the trailer?
It’s not uncommon for the turn signal and brake light to malfunction on one side (in this case, the left side) of your trailer.

That said, knowing the potential causes behind this occurrence will help you know how to deal with this problem.
Below, we take a closer look at all the potential causes behind this problem:
- Bad bulb: One of the common causes behind these lights failing is a damaged or burned-out bulb. If your turn signal light/brake light bulb appears blown, remove it from the socket and replace it with a new one.
- Wiring issues: Problems with your trailer wiring, e.g. frayed wires, damaged sections in the wiring harness, etc., can also make the lights malfunction. There could also be a short circuit in the trailer wiring. Therefore, it’s advisable to inspect your wiring for these problems and fix them.
- Bad connection: Sometimes the wiring connection that exists between your towing vehicle and the trailer may be problematic, causing the trailer lights on the side not to work. Make sure all your connections are secure, corrosion-free, and not damaged. Clean any corrosion present and secure loose connections.
- Blown fuse: You should also check the fuse related to the left trailer lights in your towing car. If it is blown, it could be the culprit behind this problem. Replacing the blown fuse with a new one with the same rating to see if the issue is resolved.
- Bad ground connections: A bad ground connection for these trailer lights, whether corroded or loose, may also be a problem. Poor grounding means electrical current can’t complete the circuit and properly power the light. As a result, the light may start flickering or even fail to come on.
How to fix your trailer left turn signal and brake light not working?

If your trailer left turn signal and brake light stops working, follow the steps below to try to resolve this issue:
- Inspect your towing car: The first thing you want to do is check if your towing car is indeed supplying power to the trailer lights. You can do so by turning your car headlights and checking if the trailer running lights illuminate as well. If they do not work, there could be an issue with the towing car fuse or wiring.
- Test the bulbs: Inspect your left brake light and turn signal bulbs. Remove them from their socket and check if they’re burned out or damaged and replace them with new ones.
If you’re not sure whether your bulbs are good, consider swapping them with those from the right side and see if they work.
Some trailers may also have dual filament bulbs, with one element for brake lights and the other one for running lights. If your trailer has this kind of bulb, check if one of the elements inside is broken.
- Test the socket: If you’ve tested the bulb and they’re working, then you may want to inspect their sockets. A multimeter will help you check the voltage at the socket when the brake pedal is activated. If there’s no voltage, the socket could be faulty or there could be wiring issues cutting off the current flow. Inspect the socket for corrosion and clean it if necessary.
- Check the wiring: Examine your trailer wiring harness for signs of damage, e.g. breaks, fraying, etc., and be sure to repair or replace them as necessary.
- Inspect the connectors: Ensure the electrical connectors aren’t damaged or corroded. Fix any loose connections and clean off any rust present.
- Test the trailer plug: With the help of a trailer light tester or multimeter, check the trailer plug for the left turn signal and brake lights. Check that there’s continuity/voltage when the lights are activated on the towing vehicle.
- Inspect the fuses: Locate the fuses related to trailer lights in your towing car and inspect them. If any of the fuses are blown up, simply replace them with new ones.
- Check the ground connection: Ensure the ground connection for the light is properly connected to your trailer frame or any other designated ground point. Clean or change the ground connections if necessary.
If the issue doesn’t resolve after following the troubleshooting guide above, then it’s time to consult a mechanic. The professionals will take your car through a more thorough diagnosis to uncover and resolve the underlying issue.
This video takes you through a step-by-step guide for troubleshooting your trailer left turn signal and brake light issue:
Video:
Can you drive your trailer with the left turn signal and brake light not working?
We don’t advise you to drive with your trailer left brake and turn signal lights not working.
As you already know, these two lights are an essential safety feature in your car. They help other drivers anticipate your movements and react accordingly—increasing your road safety.
When you drive with a malfunctioning left turning light, the drivers behind you would be confused about your intentions to make turns or change lanes. This can lead to potentially dangerous driving situations and significantly increase the risk of collisions.

Similarly, driving your trailer with a malfunctioning left brake light can also make it hard for the drivers behind you to tell when you’re slowing down or coming to a stop. This further poses safety hazards.
Still at it, it is against traffic regulations in most jurisdictions to drive your trailer with a malfunctioning turn signal and brake lights. You can get pulled over and served with a fine as well as other penalties.
Overall, if you discover that your trailer left turn signal and brake lights are not working, have them fixed before you can get back on the road again. This will minimize the risk of accidents on the road.
Why is your trailer turn signal not working when the lights are on?
Sometimes, only your trailer turn signal light will fail to work but the other lights will come on. This issue can be caused by several factors as discussed below:
- Bad bulb: Check if your turn signal bulb is burned out and replace it if necessary. Some trailers use bulbs with dual filaments to serve as the turn signal and brake lights. Check if one of the filaments inside is broken. If yes, you’ll need to replace the bulb.
- Incorrect bulb installation: If the turn signal bulb is incorrectly installed, it can also make the turn signal light stop working. For this reason, we advise you to pull out the bulb and reinstall it properly to see if it works.
- Blown fuse: You may also want to check your towing vehicle fuse box for the fuse related to the malfunctioning turn signal light. If the fuse is blown, replace it with a new one that has the same amperage rating.
- Faulty wiring: Examine the wiring leading to the turn signal switch in your trailer for breaks, fraying, cuts, shorting, etc. Fix any damaged sections to ensure undisrupted current flow.
- Bad connections: If the wiring is okay, look into the electrical connectors for loose connections or corrosion buildup. If there’s corrosion present, clean up the contacts to allow for proper conductivity.
- Faulty turn signal switch: If your bulb, fuse, and wiring are good, then the issue may be a failing turn signal switch on the towing car. If you test this switch and it appears faulty, replacing it may help fix the problem.
Why is your semi-trailer left turn signal not working?
You may also experience a situation where the left turn signal on your semi-trailer isn’t working. Several potential causes could also be behind this issue.
One such culprit would be a bad bulb that may have become damaged or burned out, causing the turn signal to stop working.
Wiring issues may also be to blame for this problem. Carefully examine your wiring for any breaks, cuts, fraying, shorting, or loose connections causing disruption of current flow to the left turn signal light.
Other potential causes to consider include blown fuses, flasher relay failure, malfunctioning turn signal switch, or grounding problems.
If you’re experiencing issues with the left turn signal and brake light not working on your trailer, it’s essential to address the problem for safe and legal operation. For more information on this topic and potential solutions, we recommend reading our article on how many brake lights are required by law. This resource provides insights into the legal requirements for brake lights and turn signals on trailers. Additionally, if you’re also encountering problems with the right turn signal and brake light on your trailer, our article on right turn signal and brake light not working on trailer may provide further assistance in troubleshooting and resolving the issue.FAQs:
There are several potential causes behind your right turn signal and brake light not working on your trailer. These include a bad bulb, blown fuse, bad wiring connection, or defective socket. Diagnosing your car will help you pinpoint the exact cause and fix it.
If the left turn signal is malfunctioning but the left brake light is working correctly, the issue could be a blown bulb, a bad socket, a problem with wiring for the turn signal circuit, or a faulty turn signal switch.
If your trailer’s left brake light doesn’t work but the left turn signal works, the potential causes to consider include a bad bulb, defective socket, blown fuse, brake light circuit wiring or connection issue, or a bad ground connection.
Conclusion
The issue of the left turn signal and brake light not working is a common experience among trailer owners and truckers. This article has just highlighted all the potential causes behind this problem, including bad bulbs, a defective socket, wiring problems, blown fuse, bad connections, and even poor ground connections.
Diagnosing your car will help you uncover the exact underlying issue causing your trailer lights to misbehave. Follow our troubleshooting guide above to easily find the culprit and fix it. This way, you can restore the functionality of your trailer turn signal and brake lights.