Headlights Won’t Turn Off? Possible Causes and Solutions

lightWhy Your Headlights Won’t Turn Off and How to Fix It

There’s no simple one-size-fits-all solution to the issue of headlights won’t turn off because every car is wired differently. Let’s take a look at the possibilities:

• Headlight switch is bad— For older vehicles where the headlight power was switched by the headlight switch
• Headlight relay contacts are stuck in the on position— For older vehicles where the headlight power was switched by relays
• Daytime running light module is bad— For vehicles equipped with a DRL module
• Body control module is bad— For late model vehicles where the headlight power is switch by the BCM and where the headlight switch is just a request input to the BCM.
• Welcome light or auto light sensor/module is bad— For vehicles equipped with auto-off headlight.

Wiring diagrams

Older vehicles using just a headlight switch

Let’s take a look at three possible wiring diagrams. In the top diagram used in older cars, power flows from the fuse to the switch. Based on whether you choose low or high beams, the switch actually switches power directly to the chosen headlights.

In this scenario, the problem is a bad switch. To turn off the headlights, locate the fuse and remove it, then replace the switch.

Late model vehicle with a body control module

In late-model vehicles, the headlight switch is just an input to the body control module (BCM). The switch contains a series of resistors that change the voltage input into the BCM. Based on the voltage input, the BCM knows which lights you want turned on.

In this setup, you may find multiple fuses; one to provide power to the multifunction switch and other fuses to power both or individual headlights.

In this scenario, you could have a bad headlight switch, a bad BCM or a headlight relay(s) that are stuck.

Pull the headlight fuses and relays to get the lights turned off right away. But you’ll need a scan tool with live data along with a multimeter to diagnose the system.

Connect your scan tool and see if the BCM is receiving the proper signal from the multifunction switch. If so, you can rule out a bad switch. Next, swap the relays to see if it’s a relay problem that’s preventing the lights from turning off. If the switch and relays check out and you determine that the BCM is providing ground to the relays when the headlights switch is in the off position, then the BCM is bad.

Late model vehicle with a body control module and DRL and Auto Lights

In this last scenario, a daytime running lights module or auto light module may be telling the BCM to turn on the lights. This one is much harder to diagnose. You’ll probably need a shop manual to test the DRL module and check out the auto light sensors and module.

In the meantime, locate the fuses and relays and remove them.

©, 2023 Rick Muscoplat