Left Turn Signal and Brake Light Not Working on Trailer

Left Turn Signal and Brake Light Not Working on Trailer

Turn signals and brake lights are among the crucial lights in a vehicle and trailer. However, these lights may sometimes stop working on the trailers, mostly on one side. In a case where the signal and brake light on the left side of the trailer stop working, there are several possible reasons.

So, why are the left turn signal and brake light not working on trailer? Some reasons behind this problem include a blown fuse, a short wire, and a faulty wiring harness. Also, the bulbs may be burned or the pins corroded, interfering with the electric current. 

The article discusses various reasons behind the left turn signal and brake light not working problem, including their causes and solutions. Read on to learn more.

Left Turn Signal and Brake Light Not Working on Trailer

Any towed trailer has federal lighting requirements and must have various lights, including brake, signals, tail, and reverse lights. The lights are crucial to help other drivers know when the vehicle is braking and turning.

Left Turn Signal and Brake Light Not Working on Trailer

The trailer gets power from the vehicle towing it using a connector usually located on its rear. However, not all cars have connectors, but users can use third-party ones.

When any of the trailer lights stop working, the problem is usually on the electrical connection. The bulbs may also be responsible. 

Reasons Why Left Turn Signal and Brake Light Would Not Working on Trailer

Reasons Why Left Turn Signal and Brake Light Would Not Working on Trailer

The reasons the left turn signal and brake light may not work on your trailer include;

1. Blown Fuse

A blown automotive fuse is one of the possible causes of why the two lights are not working on your trailer. A fuse protects the lights from excessive current, usually caused by a short circuit. When the fuse has blown, the left turn signal and brake lights on the trailer won’t work.

Diagnosis

Use a test light to verify that the vehicle has a blown fuse affecting the trailer’s left turn signal and brake light. Follow the steps below;

  • Step 1. Access your car’s fuse box. Consult the user’s manual if you can’t locate it.
  • Step 2. Locate the fuses associated with the trailer lights, specifically the left lights.
  • Step 3. Attach the tester’s ground to the battery and touch the fuse with the test light’s probe.
  • Step 4. If the test light glows, the fuse is okay, and vice versa.

Solutions

To fix a blown fuse, buy a fuse with the same amperage as the one you’re replacing and follow the steps below.

  • Step 1. Turn off the vehicle
  • Step 2. Access the car’s fuse box
  • Step 3. Remove the blown fuse using a fuse remover or your fingers
  • Step 4. Install a new fuse, ensuring it is well-seated
  • Step 5. Test the left turn signal and brake light

Replacing a fuse will cost between $20 and $70, depending on whether you do it or hire a professional.

2. Short Circuit

A short circuit, especially on the trailer, is another possible reason behind failed lights on the left side. A Short circuit usually happens due to damaged or frayed wires interfering with the current.

Trailer Short Circuit

Diagnosis

To confirm the possibility of a short circuit, check for damaged wires on the left side of the trailer. Also, use a circuit tester or a multimeter to test for continuity. Follow the steps below;

  • Step 1. Connect the negative probe to a known ground source
  • Step 2. Touch the left turn signal and brake light pin with the positive probe
  • Step 3. There’s a short if the tester beeps or there is a reading showing continuity
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Solutions

There are several solutions to short circuits causing trailer light problems. They include;

  • Fix any damaged wire by cutting and joining it with a new one.
  • Fix frayed wires using glue, electric tape, or heat shrink tubing

Diagnosing and fixing a short circuit in your trailer can cost between $120 and $250, depending on the repair work needed.

3. Burned Bulbs

Short circuits usually result in burned bulbs. The excess current can easily burn the bulb’s filaments. On most occasions, they should be the first things you check after realizing your fuses are blown.

Trailer Burned Bulbs

Diagnosis

Inspect the bulbs to confirm whether they are burned or not. Usually, you’ll unscrew the cover shielding the brake lights and the turn lights to access the bulbs.

Observe the bulbs for burnt filaments or physical damage, like cracking. Cracked glass and burnt filaments usually mean the bulb is burned or damaged.

Solutions

To fix burned or damaged bulbs, you must replace them. Follow the steps below;

  • Step 1. Unscrew and remove the cover shielding the left turn signal and brake light
  • Step 2. Remove the bulbs from the holders
  • Step 3. Replace the bulbs with fitting replacements
  • Step 4. Screw back the covers

Bulb replacements will cost you between $10 and $100.

4. Corroded Pins

Corroded pins usually interfere with various trailer functions, including lighting, by disrupting the current’s flow. The pins get corroded after exposure to moisture, which reacts with oxygen. 

Corrosion can be on some pins, and in this case, on the left side, affecting the left turn signal and brake light.

Diagnosis

Perform further diagnosis to confirm the pins in the connector are corroded and causing this problem. Follow the steps below;

  • Step 1. Switch off the vehicle
  • Step 2. Detach the connector
  • Step 3. Check the vehicle’s side of the connector for corrosion on the pins.
  • Step 4. Observe the trailer’s side of the connector for corrosion on the ports.

Solutions

Follow the steps below to fix corroded pins in a connector and fix the issue with the left turn signal and brake light.

  • Step 1. Detach the connectors
  • Step 2. Spray it with an electronic cleaner of your choice
  • Step 3. You can also soak the connectors in vinegar for a couple of hours
  • Step 4. Allow the connectors time to dry
  • Step 5. Reinstall the connectors and ensure they are well covered when not in use

Fixing corroded pins can cost below $30 if you do it yourself. However, a mechanic will cost you more than $60.

5. Loose Ground Connection

A Loose ground connection on your trailer can cause the left turn signal and brake light not to work. The contact points get dirty with time, or the wire becomes damaged, interfering with connections.

Trailer Loose Ground Connection

Diagnosis

To confirm that your vehicle or trailer has a loose ground connection, perform further diagnosis. Trace the wiring to the ground on the vehicles’ and trailer sides. Check for;

  • Corrosion
  • Loose contact
  • Broken wiring
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Solutions

The solution to a loose ground connection includes;

  • Replace any broken wire.
  • Scrap any corroded part where the ground wire connects.
  • Connect the wire to the grounding point well.

Fixing ground connection is between $150 and $300.

6. Faulty Harness

A faulty harness can cause the left turn signal and brake light not to work. The harness may be loose or damaged, interfering with the current supplied to the left side of the trailer.

Trailer Faulty Harness

Diagnosis

To confirm the faulty connection is behind the issues with the two lights, perform further diagnosis.

  • Check the wiring for broken connections on the wiring on both sides of the vehicle
  • Check wires for frayed wire

Solutions

The solution to a faulty harness is to replace or fix it. These fixes include;

  • Cut the broken wires
  • Add new pieces to the cut wire
  • For frayed wires, use an electric tape

The cost of replacing the harness is $100 and $400.

Having your trailer’s left turn signal and brake light malfunction can be a significant hindrance, especially when you’re on the road. However, it’s essential to note that such issues aren’t exclusive to trailers. Many drivers face challenges where the turn signal and brake light aren’t working on one side of their vehicle. Moreover, there are instances when only the brake light is not functioning on one side. Familiarizing yourself with these common problems can help you diagnose and address them more efficiently.

FAQs

Here are some related questions to help in your research about the left turn signal and brake light not working;

Q1. Can Insufficient Current Flow Cause The Left Turn Signal and Brake Light Not to Work?

Yes. Insufficient current flow can cause the left turn signal and brake light not to work. However, the lights usually dim or affect both sides of the trailer unless a loose connection causes it.

Q2. Can an Issue with The Control Module Cause The Left Turn Signal and Brake Light Not to Work?

Most modern vehicles have an electric control module in the trailer that controls the lighting and electrical connections. If this module malfunctions, it may cause issues with the left turn signal and brake light.

Q3. How Long Does Diagnosing and Fixing the Trailer’s Left Turn Signal and Brake Light Not Working Problem Take?

Most repair shops can diagnose your vehicle and tell you the cause of the left turn signal and brake light not working within an hour. With experience, you can also diagnose the problem within an hour. However, the repair time will vary with the cause of the issue since some solutions are complicated. 

Bottom Line

The trailer’s left turn signal and brake light not working problems usually point to an issue with the connector. The connector may be corroded or loose, interfering with the electrical current flow. However, a blown fuse may also be the cause as a result of a short circuit.

To handle the issue effectively, diagnose further the problem to pinpoint the cause and provide an appropriate fix. Most diagnosis and repair works are easy and doable without a professional’s help unless you’re totally clueless. However, take the vehicle to a mechanic shop if you can not figure out the problem.

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