Several reasons might cause the headlight of your vehicle to remain on, with most of them being identifiable within a mere few minutes. The need for a mechanic to decipher the causes might not be necessary and you might even be capable of figuring out and applying the solutions independently, assuming you have several hours devoted to your vehicle’s electronic maintenance and repair.
Headlights are more troublesome when they do not work. This is a common issue that most vehicles will fix without trouble. However, it can become quite confusing if you find your headlights stay on when they are meant to be off. It is even more so when one of them is on, and the rest have shut off.
Causes can include simple issues like a malfunctioning headlight switch or as complex as a malfunctioning automatic light system. We will take you through quick fixes to help you save your vehicle’s battery when the light fails to turn off. We will also tell you of the causes that might let your headlights stay on and how to find solutions to these causes.
What do you do if your car headlights won’t turn off?
You have a few options when your headlights refuse to turn off. These are not long-term fixes but quick fixes that can help you save your vehicle’s battery from being drained. You do not need to be an expert mechanic to apply these fixes, but it would be helpful if you knew your way around simple vehicle repairs.
The three options that you have when your headlights cannot turn off include:
- Removing the headlight fuse of the specific headlight.
- Disconnecting the headlight relay.
- Disconnecting the cables from the battery.
Option 1: Disconnect the headlight fuse
Disconnecting the headlight fuse is pretty simple and won’t take too much of your time. All you need to do is look at your vehicle’s manual to locate the fuse box. You need the manual to locate the specific fuse box for your headlight since most cars have several fuse boxes.
Proceed to pop off the top of the fuse box and take off the fuse with two fingers. Please do this by pulling it outwards and wiggling it gently to avoid damaging the fuse and box system. You will now notice that the headlight has turned off. This is the sure way of fixing the issue till you find a cause for the problem.
Option 2: Disconnecting the headlight relay
Bad relays are some of the problems that will cause the headlights to stay on in your vehicle. We will talk about why that is in the next chapter. Here, we will show you how to disconnect the headlight relay to prevent the battery from dying.
A headlight relay is located under the hood. It is connected to the onboard computer to be programmed to keep your headlight on for a particular period. This period is usually 1 to 3 minutes depending on the make and model of your car.
Quick Tip: Do not disconnect the relay till the delay period of your vehicle is over. As a rule of thumb, give it five minutes.
Use the owner’s manual to locate this relay and gently tap the case, and wiggle it out of place. The headlight should have been turned off if this process works. Remember, this is a temporary fix since you haven’t located the issue causing the headlight to stay on.
Option 3: Disconnecting the cables from the battery
Disconnecting the battery is the last option since it may cause issues if you are not well-versed in the process. You may end up erasing the onboard computer’s memory, affecting how well it can analyze factors like fuel economy. Some vehicles provide a security code that can help prevent this from occurring when you disconnect the battery. Remember to check for that special code.
You will also need to pay attention to the cables to avoid short-circuiting the battery. Disconnect the negative battery cable, which is typically black and is connected to the – symbol on the battery. Ensure the cable doesn’t touch the now naked battery contact since there is a slight chance it may cause a spark and maybe an explosion. The headlight will turn off since the battery is not connected anymore.
The issues leading to the headlights won’t turn off
Now that you know the quick fixes to shut off a headlight that won’t turn off, let’s look at the causes. Some of the issues need a professional with expert tools like multi-testers to ensure they are in good working condition. Others can be diagnosed with a simple electric check and turning of a switch. Here are the six issues that lead to headlights that won’t turn off.
1. Malfunctioning headlight relay
Headlight relays are technical systems connected to the onboard computer to control the light emitted by the headlights. They are often used to control the high beams and low beams. The control process is done with the help of an electromagnetic switch that utilizes a low current to regulate a higher current circuit.
Relays are used in a wide range of applications, but they regulate electronic systems through the programs on the onboard computers. Like all relays and electronic systems, the headlight relay can malfunction and eventually fail due to a few reasons like old age, physical disturbance, and water damage. If the headlights stay on or refuse to turn on, you may have bad headlight relays.
The easiest way to know if you have a bad relay is to swap it out with a new/functional relay with the same design and specs as the old one. You will need the owner’s manual to locate the headlight relay. It is typically located in the power distribution box in the engine bay. All you need to do is disconnect it gently to avoid damaging the system.
Replace it with the new/functional headlight relay. A new relay will usually cost you less than $30, which is a low price for fixing the issue. If the issue is resolved, you know you had a bad relay. If the issue persists, then you can return the old relay to its socket and diagnose other issues that may cause your headlights to stay on.
Read more: Low beam vs. High beam: When should I use them?
2. Failed daytime running light module
DRLs, Daytime Running Lights in full, are lights invented in the 1980s in countries that usually experience dim daytime during snow and other environmental situations like rain and fog. They are dimmer than your other headlights and are intended to let other drivers see you on the road to avoid accidents.
Credit: f150forum.com
The Daytime Running Light module controls these lights by receiving a signal from the ignition when you turn on your vehicle. The DRLs will be turned on once the module receives the signal. It will then keep the lights on while your vehicle runs. The DLR module may malfunction if the running headlights stay on constantly even when the engine is off.
In this case, you will need to take the vehicle to an expert mechanic to replace the module. This is the only way to fix Daytime Running Module malfunctions. The headlights will turn off if the module is causing the issues.
3. Faulty headlight switch
Malfunctioning headlight switches can cause many issues to the headlight, including letting them stay on and having inconsistent high beams. The headlight switch is widely known as the dimmer switch; it is an electronic knob device that controls the headlight functions. It lets you switch between auto mode and regulate the light between various methods depending on your vehicle.
The headlight switch can either be a knob or a button, but most designs tend to get stuck. This is more so in older vehicles whose headlight switches have been operated multiple times in their lifetime. It may seem too obvious to notice, but sometimes a stuck knob can be easily overlooked, resulting in expensive repairs.
If your headlight switch is stuck or worn out, you get it replaced with an operational one. The inspection of the switch is easy since all you need to do is try and switch between various modes to see how the lights respond. If all modes are working properly, you do not need to replace the switch. Otherwise, proceed to take your vehicle to a professional who will replace the switch.
4. Failed multifunction switch
The multifunction switch, also referred to as the combination switch, operates various components in your vehicles. Its functions include controlling the high beams and low beams of the headlights. It is also used to control the turn signals as well as the wipers.
You will find the multifunction on the left side of the steering wheel in most vehicles. It is easily accessible by the vehicle driver for convenience. You will notice that the multifunction switch is failing if you experience several issues with its associated controls. That is the turn signals, wipers, and headlight functions.
A failed multifunction switch will affect the headlights by sticking to one mode, whether off or always on. This is usually because the switch is worn out or broken. The only solution to this issue is to replace the failed switch with a new one. Take the vehicle to a licensed professional to diagnose the switch and find a replacement part for it.
6. Bad light sensor
Automatic light sensors are convenient as they eliminate the need for the driver to turn on the headlights at dusk, night manually, or dawn. It also helps illuminate the road automatically when the weather conditions are not favorable during storms or snow.
The light sensor is typically located on the windshield in a not easily visible place. You can check behind the rearview mirror if you are looking for it. Or on the dash close to the edge of the windshield. Or next to the rain sensor on the vehicle’s windshields.
Malfunctioning light sensors will tend to stick to one mode, in this case letting the headlights stay on even when there aren’t any visibility issues outside. In some cases, you may find that the lights stay on and work perfectly in others.
The light sensor may fail for a few reasons, like wiring issues and broken components. You will need a professional to inspect this sensor to know whether you need a replacement part or just a quick wiring fix.
7. Damaged grounded wire
The bad ground on the headlight indicates a problem with the ground circuit to the headlights. The purpose of the ground wire is to direct electricity to the negative terminal of the battery from the vehicle’s headlight. This makes the connection between the headlight and the battery for power.
You will find this wire connected to the vehicle’s chassis close to the headlight. It is typically short. In case it is damaged, the ground wire can cause lighting issues that result in the headlights staying lit. You will need to test it using a multimeter to see if it is working properly.
The multimeter will measure the resistance to check for continuity. No continuity means the wire is not connected properly or is damaged. You will need to replace the wire or repair it if it can be fixed for the headlight to go off when intended.
What should I do if one headlight is on when my car is off?
Automatic light sensors that are malfunctioning are the major cause of this problem. However, ensure you check if one of the headlights is burnt out before diagnosing the light sensors. Faulty light sensors may cause the headlights to get out of sync with one another. This means one may end up staying on even when it’s shutdown time.
All you need to do to fix this problem is use the parking brake. Once you notice the bulb turning off when you use the brake, then you can conclude a faulty automatic light sensor is the issue. Proceed to replace it.
The cost of fixing the headlight issues
Headlight issues are not severe issues in terms of the cost of repair. However, this depends on the issue causing the headlight to stay on. If a bulb is damaged, you can replace it for less than $30. Wiring damages will cost you less than $10, provided you repair yourself.
A bad automatic light sensor may be the most expensive issue to fix in this case. You will spend about $300 to $400 to get a replacement, and the repair charges to the mechanic will add this up depending on the store.
Conclusion
It is easy to diagnose and fix issues that cause your headlights to stay on. Most of the causes do not require advanced skills, and you will not need advanced equipment either. However, ensure you have your owner’s manual in hand and ready to visit the local mechanic shop for part replacements.
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