Headlights won’t turn off

Headlights won’t turn off — How to fix

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
• Headlight relays contacts are stuck
• Daytime running light module is bad
• Body control module is bad
• Welcome light or auto light sensor/module is bad

Headlight wiring diagrams

Older vehicle using just a headlight switch

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

If the headlights won’t turn off in this scenario, the problem is a bad headlight switch. To turn off the headlight, locate the headlight fuse and remove it. The replace the headlight 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 headlight 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 headlight switch and other fuses to power both or individual headlights.

In this scenario, if the headlights won’t turn off, 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 headlight 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 headlights. 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 headlight fuses and relays and remove them to turn off the headlights.

©, 2023 Rick Muscoplat