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  • Faulty bulbs, a dead car battery, and a bad alternator are common causes of a malfunctioning turn signal bulb.
  • Replacing your turn signal bulb by yourself can be a complicated process because you’ll have to remove parts that are obstructing the bulbs, such as the trim, body pieces, and other components, so be sure to check your vehicle’s repair manual.
  • If you’re certain that your bulb is good but the turn signals still aren’t working properly, there might be a problem with your vehicle’s flasher relay, turn signal switch, or electrical system.

Not only is it frustrating to drive with broken turn signals, but it is also dangerous.

With that said, it’s essential to understand how and why your vehicle’s turn signal bulbs burn out or malfunction.

Here are some of the most common reasons why a turn signal bulb may malfunction:

  • Faulty turn signal bulb
  • A dead car battery
  • A bad alternator
  • Malfunctioning turn signal switch
  • Issues with the electrical system

What Causes a Turning Signal Bulb to Malfunction?

Your turn signal lights might malfunction in a variety of ways. For example, they could start flickering, or they could stop working outright. You can also tell if something’s wrong with the bulb if the turn signals start flashing. Generally, signals will flash on the side with the bad bulb.

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If you’re curious about some of the many different explanations as to how a vehicle’s turn signal bulbs could go wrong, read on.

You can also tell if something’s wrong with the bulb if the turn signals start flashing. Generally, signals will flash on the side with the bad bulb.

Anthony Harlin, ASE Certified Master Automobile Technician

Faulty Bulbs

Carefully inspect your turn signal bulbs for burnt, darkened areas as well as signs of corrosion or other damage. If you hear rattling coming from inside the bulb, then the filament within might be broken.

If your bulb is damaged, it’s far easier and far more reliable to replace it than to try and repair it.

Dead Car Battery

The car battery is what powers all the electrical components of your vehicle, including the turn signal bulbs. If the car battery runs out of power, then your turn signal bulbs won’t be able to light themselves up.

If you have issues with electronic parts of your vehicle like the lights or the radio, you might want to check the health of your car battery.

Bad Alternator

The alternator is what charges the car battery as you drive. A bad alternator struggles to produce the electricity necessary to keep the car battery fully charged, meaning you might face problems like malfunctioning electrical components. This includes your turn signal bulbs.

Malfunctioning Turn Signal Switch

If your turn signal bulbs don’t appear burnt out yet don’t work properly, the problem might lie in the switch. Check the turn signal switch for broken or cracked plastic, corrosion, or loose connections. If your switch is broken, then it’s time to replace it.

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Problems In the Electrical System

The electrical system is what relays power from the car battery to the various electronic components of your vehicle. If the wires get displaced or if any fuses blow out, there’s a good chance the electrical system will malfunction and cause various parts of the vehicle to malfunction—turn signal bulbs included.

Carefully inspect the wires and the connections of the turn signal bulbs to make sure everything is in the right place. It’s also important to keep a sharp eye out for any signs of damage so you can replace any parts that are beyond repair.

How to Replace a Turn Signal Bulb

Turn signal bulbs may burn out and require replacement over time. Here’s a quick guide to what the replacement procedure might entail.

Before doing any repairs on your vehicle, make sure to check your vehicle’s repair manual. If you’re pretty new to auto repairs, you can consult a mechanic or someone with advanced DIY knowledge.

  1. Park your vehicle.
  2. Lift the trunk or the hood of the vehicle, depending on which turn signal bulbs (front or rear) require replacement.
  3. Remove parts of the vehicle obstructing the way such as trim, body pieces, and other components.
  4. Disconnect the wires of the old turn signal bulbs before removing the component.
    • Bear in mind that not all bulbs are removed the same way. Some pull out straight, whereas others need to be pushed in.
  5. Install the new turn signal bulbs. Avoid letting any contaminants such as oil or dirt into the assembly.
  6. Connect the wiring to the new turn signal bulbs.
  7. Test the lights to see if they work properly and make adjustments if necessary.
  8. Reinstall the parts that were removed to access the turn signal bulbs.
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Frequently Asked Questions

What Should I do if the Turn Signal is Not Working but the Bulb is Good?

If you’re certain that your bulb is good but the turn signals still aren’t working properly, there might be a problem with your vehicle’s flasher relay, turn signal switch, or electrical system. Carefully inspect each of these parts as well as the wiring connecting the turn signals to the electrical system for any signs of damage.

How Long Does a Turn Signal Bulb Last?

On average, a turn signal bulb should last you up to 4,000 hours. Of course, this number could either increase or decrease depending on your driving habits. If you drive frequently and use your turn signals a lot, your vehicle’s turn signal bulbs might burn out sooner rather than later.

Should You Replace Both Turn Signal Bulbs At the Same Time?

Yes, it’s strongly recommended to replace both turn signal bulbs at the same time. This way, If one goes bad, the other will likely follow shortly afterward.

It’s also a good practice because having the two bulbs replaced at the same time means you can guarantee that the intensity and color of the beams will match. If you replace the bulbs one at a time, you won’t be able to completely guarantee that you can get evenly-matched beams.

About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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