Despite the many advances in motor vehicle technology, the basic lighting set up in your car has remained largely unchanged. When your car’s lights won’t turn off, the trouble-shooting process is pretty much the same as it has been for many years.
Firstly, don’t leave your car with the headlights on overnight. They will drain your battery and you’ll have the additional headache of a dead battery to deal with in the morning.
The simplest solution is to remove the headlight fuse until you have time to fix the problem. You’ll find the fuse under the dashboard or in a fuse box under the hood. The fuse box cover has a diagram that indicates which fuse relates to each part of the electrical system.
Locate the headlights fuse and remove it carefully.
Alternatively, you can remove the headlight relay, if it is more accessible than the fuse.
The relays are the larger, rectangular boxes next to the fuses in the fuse box. They handle much higher electrical loads than the switches, so removing the relay breaks the circuit between the battery and the headlights in the same way that removing the fuse does.
If that doesn’t work or you can’t find the correct fuse or relay, then disconnect the battery cable at the battery terminal.
Locate the negative battery terminal; it’s the black one. There is also a (-) sign next to the battery terminal in case you’re in any doubt. Loosen the nut holding the clamp tight and pull the clamp off the battery.
Once removed, make sure that the cable cannot accidentally contact the negative battery terminal to avoid the current from flowing again. Bear in mind that if you disconnect the battery, it may clear settings in your car’s electronic control unit which will require some time to reset once you reconnect the battery.
Typically, there are 5 components in a car’s lighting circuit.
If your headlights are on and won’t switch off, then it is clear that the battery, fuse, and bulbs are functioning fine. The problem is then to isolate either the switch or the wiring.
Let’s look at each one of the possible causes:
Try switching the headlights off before switching the ignition off. Some modern vehicles have light systems designed to remain on for a short period after you have turned the ignition off. If the lights switch off before you turn off the ignition key, then your problem is the module that delays the lights turning off.
If your vehicle is fitted with daytime running lights, then the module that controls the system can be deactivated by setting your parking brake.
If the lights remain on with the parking brake engaged, then you can try replacing that module to resolve the problem. It is also possible to remove the module completely so that the feature is permanently disabled.
Your headlight switch may also have shorted out, resulting in a build-up of heat. If the heat melts the insulating cover around the wires or the plastic inside the switch mechanism, then the wires may make contact, completing the circuit and causing your headlights to remain on.
Related to the headlight switch is the relay. The relay is a magnetic switch that can burn out.
As there are similar relays used for various systems in the electrical circuit, you can try another relay that is identical to the headlight one and test the headlights. If the headlights switch off, then you can purchase a replacement relay to solve your problem.
For vehicles fitted with a daytime running light module, the checks needed to test this as a potential problem are a little more complex.
The relay connected to the daylight running module picks up input from a variety of sources within your vehicle. These sources include the parking brake, the headlight switch, one or more diodes as well as indicator lights on your dashboard.
If you can read a wiring diagram and have access to test light and multimeter, you can check the continuity of the various circuits and components. But if you aren’t an experienced DIY enthusiast or auto electrician, then it’s best left to the experts to check exactly which component is faulty.
If your vehicle is fitted with automatic headlights, then a sensor is located in the front of the car which switches your headlights on when the sun goes down. These sunlight sensors are either located in the middle of the plastic cover below your windscreen or it is positioned under the windscreen in the vicinity of your rear-view mirror.
A quick way to check if this module is potentially the answer to your question; “why won’t my headlights turn off”, is to turn the headlight selector switch from auto to off or “0”.
If the headlights switch off, then you’ve located the problem.
If the taillights are on, we know that the battery, fuse, and bulbs are working, which leaves switches and wiring as the potential culprits.
The brake light switch is located under the dashboard adjacent to the brake pedal. As the switch is open when driving and closed when applying the brake pedal, we can assume that the switch may be stuck in the closed position.
To check this, locate the brake switch and notice if the brake lever moves in unison with the brake as it is depressed. If the switch remains stationary, then you can be certain that it is contributing to your problem.
There’s a lot of dirt and moisture found in the footwell around the pedals, and switches can get gummed up. Using a rag, clean off the switch and any oil or muck that may be preventing the switch from moving.
Disconnecting the switch will confirm that it is the problem if the lights turn off when you separate the connection.
If that doesn’t work, then try disconnecting the switch. If that works and the brake light turns off, then replacing the switch should solve the problem.
If disconnecting the switch doesn’t fix the problem, then you may have worn wiring that is causing a short.
Having your turn signal stay on can be a serious safety issue. It may either continue to blink or it may just stay on without blinking. If your turn signal stays on after the indicator stalk has returned to its central position, then you may be dealing with a bad flasher relay, a faulty turn signal switch, or possibly a grounded wire.
The turning signal may stay illuminated on one side only. This can indicate a blown bulb on the other side. But it is usually accompanied by rapid blinking. Replacing the dead bulb will confirm the diagnosis.
The turn signal relay is normally located under the dashboard. If the turn signal lights switch off after removing the relay, then replacing it may solve the problem.
There is a spring inside the turn signal that returns the switch to the off position as the steering wheel is centered after making a turn.
If the spring is worn or broken, then replacing it will solve the problem of your turn signal staying on.
If the turn signal switch and relay are not the problems, then it’s highly likely that the wiring has become worn and is shorting out the circuit.
The danger with a short is that it can drain the battery, damage components, and, in the worst-case scenario, start a fire. A sure sign that you have a short circuit due to a grounded wire is when you remove the turn signal fuse and the lights stay on.
Unless you have experience dealing with worn wiring, it is best to remove the turn signal bulbs and take your car to an auto-electrician to repair the problem professionally.
Depending on the age of the battery and the number of lights that have been left on, it could take between 4 and 8 hours to drain the battery on a car.
Yes, interior lights do turn off automatically unless you have set the switch to the permanently on position. In that case, the lights will remain on until you switch them off. Some modern cars have a sensor that will turn the interior lights off after a while if the vehicle has not been started. This is done to ensure that the battery is not run down.
The dome light switch can be accidentally bumped or adjusted in error, so check its position first before moving on to the next fault-finding step. Opening and closing the doors may trigger the dome light and it will usually extinguish once the vehicle has been driven for a short time.
The interior light switch may have been set to the permanently on position or the door switch may be broken and require realignment or replacement.
Some cars have a parking light feature that illuminates the park lights by engaging the turn signal on one side of the vehicle. Returning the turn signal to the central position will switch the park lights off.
Some European cars are known to have problems with the rear headlight leveling sensor that causes the park lights to stay on. Replacing the sensor solves the problem.
Some modern cars are fitted with a delay feature that can take a few minutes to switch the headlights off after switching off the engine.
You should check if your sunlight sensor is working. Often, when work is carried out on a car’s windscreen or window wipers, the sunlight sensor is left unattached. Alternatively, you can select the off position on the headlight switch if it was set to automatic.
There are many reasons why the lights stay on when a car is off. But, as with most electrical problems, it can be frustrating to find a solution. We hope that you found the advice and tips we shared in this article useful when your car lights won’t go off.
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