Are you unable to turn off one or both of your vehicle's headlights? Allowing your vehicle's headlights to run 24/7 is never a good idea. Whether they are halogen, light-emitting diode (LED) or high-intensity discharge (HID), they will consume power. The alternator will keep the battery charged while you are driving. After turning off your vehicle, though, the alternator will stop charging the battery. And if the headlights are still running, they'll continue to draw power from the battery -- eventually depleting the battery of its charge.
Faulty Headlight Switch
A faulty headlight switch can prevent your vehicle's headlights from turning off. Headlight switches, of course, are circuit-controlling devices that either allow or interrupt the flow of electricity to a headlight. All headlights require an electrical connection. Headlight switches are found within these connections.
When you turn on your vehicle's headlights, the switches will create a complete circuit while allowing electricity to flow from the battery to the headlights. When you turn off your vehicle's headlights, the switches will break or interrupt this connection. If a headlight has a faulty switch, it may continue to receive electricity from the battery, in which case the headlight may not turn off.
Daytime Running Lights Failure
If your vehicle's daytime running lights have failed, you may struggle to turn off the headlights. Daytime running lights, of course, aren't the same as regular headlights. They are smaller, dimmer bulbs that are designed for use during the daytime. Many vehicles have daytime running lights that run automatically during the day.
Daytime running lights have modules, and failure involving these modules can prevent the headlights from turning off. Not all vehicles have daytime running lights. Nonetheless, if your vehicle features daytime running lights, you should consider checking the module. If the daytime running lights module has failed, you may not be able to turn off the headlights.
Electrical Wiring Problem
Problems involving your vehicle's electrical wiring can prevent the headlights from turning off. Headlights are connected with wires. While the wires are insulated, they can deteriorate over time. The protective jacket may develop a tear that exposes the inner conductor to the surrounding elements.
You should check the wires with which your vehicle's headlights are connected. Make sure they aren't torn or otherwise compromised. Using a multimeter, you can also test the wires.
From faulty headlight switches and daytime running lights failure to electrical wiring problems, there are several possible reasons why your vehicle's headlights won't turn off.