Introduction
If you ever face the issue where both headlights stop working, then it can be more than just an inconvenience. In fact, this can cause a serious safety issue. For instance, if you drive without working headlights, it will put you at risk, especially at night or in poor weather.
Not only will it reduce your visibility, but it will also make your vehicle difficult to see for others. Furthermore, in many countries, if you drive without headlights, it will be considered a crime and you will end up paying fines.
This is one of the reasons why you should fix both lights not working as soon as possible if you ever get stuck in the darkness while driving. This guide explains how headlights work, why they fail, and how you can troubleshoot and prevent future issues.
How headlights normally work
Let’s break down how a headlight simply works to understand the factors that you can check when they are not working.
- Battery: This component helps to supply the electrical power that runs the car and its lights.
- Fuse: This will protect the headlight circuit from short circuits and overloads. If the current flow is too much, the fuse blows to prevent damage.
- Relay: This one works like a switch that regulates high current using a low-current signal. This prevents the headlight switch from burning out.
- Headlight Switch: The part you use to turn on headlights or switch between low and high beams.
- Wiring & Grounds: This carries electricity from the battery to the bulbs and completes the circuit back to the battery.
- Bulbs: This is the final component that turns electricity into light.
Now that we talked about the components that make the headlight work, let’s get into the issues that can break down your headlight rather than the bulb unit.
Reasons both headlights are not working
1. Blown Main Fuse or Faulty Relay
Both headlights are connected to a fuse or a relay, and if either of them stops working, it will automatically cut the power to both bulbs. Fuses are easy to replace and not very expensive. However, a faulty relay might need some test runs and replacement done by a professional.
2. Wiring or Ground Connection Issues
In order for a headlight to function, there needs to be a solid ground connection alongside a good wiring system. This issue can show up after a period of time when the wires are fraying, corroding, or loosening due to heat, moisture, or vibrations. Many drivers may overlook this common weak ground connection.
3. Switch Failure of Headlight
There is also a possibility were the headlight switch can fail internally. This is a very common issue in old cars, as it carries more current. However, the same issue can also be seen in new vehicles, as they can fail due to wear and tear despite switches sending signals to a control module.
4. Battery or Alternator Problems
If your battery is weak or the alternator isn’t charging properly, you will notice that the headlights may dim, flicker, or go out completely. Also, if you notice that other electrical systems (radio, AC, dashboard lights) are also malfunctioning, this can be a strong clue to recognize this issue.
5. Newer Cars Facing Control Module Malfunction
Talking about the new cars, they usually rely on a body control module (BCM) to regulate lights. A software glitch or electronic failure can disconnect power to both headlights. Sometimes, a simple system reset helps, but other times the module must be replaced.
Why bulbs are mostly not culprits
A lot of people might assume that both bulbs stopped working at the same time because they burned out – at the same time! While this is possible, it is also something very rare to happen. Bulbs have independent lifespans, and usually, one fails before the other – even if you have installed both at the same time.
Unless you’ve been using very old bulbs or driving with daytime running lights that wear out faster, both bulbs are rarely the issue. That’s why, before replacing bulbs, it’s smart to check fuses, wiring, and power supply first. It is worth noting that LED headlight bulbs last longer compared to halogen bulbs.
If you notice that bulbs are the reason causing the issue, then you can always go to an online automotive lighting store to get good quality ones.
Troubleshooting steps
1.Check Fuses and Relays
Simply open the dashboard of your fuse box and find the headlight fuse. If it’s blown, replace it with one of the same amperage. Now, you can test the relay by swapping it with another similar relay from the fuse box.
2.Test the Headlight Switch
After this, you can check the switch. A mechanic can test whether it’s sending power to the circuit when engaged.
3.Wiring and Ground Connections Check
It is recommended to check for corrosion, especially near the headlights themselves. Check connectors for looseness or burning marks. Clean the ground point with sandpaper if it looks rusty.
4.Check Battery Voltage and Alternator Output
For this, you simply use a multimeter. If readings are lower, the alternator or battery may be failing. If the car is off, then the battery should read ~12.6 volts; otherwise running car should read 13.5–14.5 volts.
5.Warning Lights on the Dashboard
Many modern vehicles show symbols on the dashboard when there is an electrical or lighting problem. It is recommended not to ignore these indicators as they’re often the fastest clue to what’s wrong.
By following these steps, you can narrow down the cause before visiting a mechanic, saving time and money.