Driving at night can be a challenging experience, especially when your headlights turn off unexpectedly. Trying to drive down a dark road with no headlights is an experience. No more needs to be said. While there are many reasons why headlights may turn off while driving, they don’t usually turn off per se; they dim and appear off, especially when driving in the dark and can’t see more than a yard or two in front.
One of the most common reasons for headlights to turn off while driving, or at least appear as they have, is a faulty alternator. The alternator takes over, providing the electrical power from the battery once the car is running; it’s also responsible for charging the battery simultaneously. If the alternator fails, the headlights will not be at their brightest. Another common cause is a blown fuse or a loose electrical connection, but if either of these is to blame, the headlights may switch off and only come back on once the problems are rectified. But there’s more on this below.
Causes of Headlights Turning Off While Driving
Dead battery
Although the battery doesn’t directly keep the headlights on while driving, that is the alternator’s job. If the battery is flat or draining its charge, the alternator will work overtime to top it back up. Because the battery is hogging all the charge, so to speak, the headlight can dim so much that you may think they have turned off. You may notice other issues such as the dashboard lights getting dimmer, the radio not working, electric windows failing to operate, and the battery charging light may be illuminated on the dashboard.
Faulty alternator
The alternator’s job is to charge the battery and provide power to the headlights and all other electrical components once the car runs. If the alternator is not putting out the correct charge (between 13.4 – 14.4 volts), issues with electrical components, such as the headlights turning off or becoming dim, will be apparent. It might not be the alternator specifically causing the problem it could the pulley or serpentine belt.
You will also experience other issues similar of that to bad battery, electrical components not working correctly such as electric windows struggling.
Loose or corroded connections
The headlights are connected to the main wiring harness through a series of connections and wires; if they are loose or the terminals at the headlight are loose, the headlights will not get a good connection, and the flow of electricity will be insufficient to keep the headlights on. Also, the back of the headlights usually has a dust and water cover; if missing, moisture can get to the back of the bulb and cause its connector to corrode. This will also cause a bad connection, and the lights may work one minute and not the next.
Failed headlight switch
A failed headlight switch (the switch in the cabin you operate) is another possible cause of headlights turning off while driving. If the switch is not working correctly, it may not be able to supply power to the headlights consistently, causing them to turn off unexpectedly. A problem with the headlight switch is that the contacts inside the switch fail, so when you turn the switch expecting it to operate, you are just turning fresh air inside the switch, and nothing is happening.
Blown a fuse or relay
When you operate the switch in the cabin to turn the headlights on, the coil inside the relay energizes, which then sends electricity to switch on; Headlight relays used to fail regularly, although most are rated for about 200,000 cycles now. You still get the odd problematic relay.
Equally, the fuse the electricity passes through can blow if the current exceeds the fuse rating, breaking the thin track inside.
Symptoms
Dimming headlights
One of the most common symptoms of you thinking the headlights are turning off while driving is they are dimming. Dimming headlights occur when your headlights lose their brightness and become less intense. This can happen for a few seconds, minutes, or permanently.
A battery or alternator-related problem most commonly causes the dimming of headlights. Another not-so-common cause in everyday cars, but more so in large trucks, is an incorrect bulb fitted to the vehicle. For example, if the car is 12 volts and a 24-volt bulb is fitted, the bulb will work but won’t be very bright.
Flickering headlights
Another symptom of headlights turning off while driving is flickering headlights. Flickering headlights occur when your headlights turn on and off rapidly.
This indicates a loose connection, usually where the bulb connects to the wiring loom. Another problem that can happen is the electrical supply needs to be more consistent, and the relay is chattering (not getting a full 12volt). Flickering headlights can be dangerous as they can distract other drivers on the road.
Headlights turning off
The most severe symptom of headlights turning off while driving is when your headlights turn off completely. It can happen suddenly and without warning, leaving you in complete darkness. Other symptoms of headlights turning off while driving may include dashboard lights flickering, the radio turning off, or the engine stalling.
The headlights switching off completely can sometimes be traced to a bad battery or alternator, but most commonly, there is something wrong with the headlight switch or a loose connection.
Preventing the Headlights From Switching off While Driving
Regular maintenance of the headlights might sound silly, and you can’t stop the headlight from switching off in case of a problem. But a quick check every month to ensure all the bulbs are operational will prevent a few issues from happening. This might mean you never have to contend with driving with the headlight bulb not working.
- Replacing blown bulbs immediately will stop any overloading on the car’s electrical system.
- Cleaning the headlight lenses will prevent any obstruction to the beam
- Adjusting the headlight alignment to ensure the beam is not high or pointing too low. Have a mechanic adjust this if you need to know how high/ low is optimum.
How to Stop the Headlights From Switching off While Driving
If you notice that your headlights are turning off while driving, first, try turning your headlights on and off again to see if they will turn back on. If this does not work, try switching to your high beams or using your fog lights if you have them. If none of these options work, it is best to pull over to a safe location and address the issue.
It will likely be because of a faulty component. Diagnosing and replacing the defective part is the only way to solve a headlight problem.
| Component | Signs of Failure |
| Headlight Switch | Headlights turn off intermittently or fail to turn on at all. |
| Alternator | Headlights dim or flicker while driving, and the battery warning light comes on. |
| Battery | Headlights dim or turn off completely, and the car won’t start. |
| Fuses | Bulb Headlights fail to work at all. |
| Bulb | One headlights fail to turn on. |
Is It Safe to Drive With the Headlights Turning Off?
The safety of driving with your headlights off depends on the circumstances. If you are driving on a well-lit road and it is not too dark outside, you can see well enough to continue driving safely until you can pull over and address the issue. However, it is unsafe to continue driving if you are driving on a dark road with no streetlights.
It is important to note that driving without headlights is illegal in most countries; it can land you in some trouble and even a fine. If your headlights turn off while driving, addressing the issue immediately is vital to avoid potential safety hazards and legal consequences.
Conclusion
Headlights turning off while driving can be a severe safety issue. It is crucial to take immediate action when this happens to prevent accidents and injuries. This problem has several potential causes, including faulty wiring or switch, a bad alternator, or a failing battery.
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