headlight not working

Why Headlight is Not Working – Bulb OK

A blown fuse causes most headlight failures. Other common problems include a bad relay, switch, or module. Wiring problems, especially inside the headlight, can also cause a headlight to stop working. In this guide, you will learn how to diagnose headlight problems. For example, in cases where you have replaced the light bulb, one of the headlights is not working.


  • One headlight doesn’t work
  • Highlight not working bulb, ok
  • One headlight is not working on the low beam.
  • Headlight not working after replacing the bulb.

Possible Causes

  • Blow light bulb
  • Blown fuse
  • Bad relay
  • Damaged wiring harness
  • Faulty light switch
  • Defective light module

Troubleshooting Steps

Check Fuses

checking vehicle fuses

Check the fuses if one or both headlights don’t work after you replace the bulbs. The low and high beams have their designated fuses for each circuit. In some car models, you will have a separate fuse for the left and right low beams.

check low beam high beam relay

Locate the fuse box under the engine and by the dashboard. Find the fuse for the low beam and the high beam. Check the fuses if your lights work on a high beam but not a low one. Fuses are very inexpensive and easy to replace. If you find a burned-out fuse, order a box of 120 assorted fuses online and replace the burned fuse with the same color, which should also be the same ampere rating.

Check Headlamp Wiring

light bulb problem

Carefully inspect the contact at the light bulb’s terminals and the wiring inside the headlight. In the picture above, you can see how the insulation melted.

damaged headlight wiring

In this picture, you can see how damaged wires inside the headlight had to be repaired.

Light Switch

bad headlight switch

Another possible issue could be a faulty headlight light switch.

The light switch on the dash turns on the light, but switching between low and high beams is performed with the lever on the steering wheel column. This is known as the multi-function combination switch, which is typically integrated with the turn signal switch.

To replace the multi-function combination switch, it is required that the steering wheel is removed. This is a Do-It-Yourself project and should take you no more than two hours. An experienced mechanic should be able to replace the switch in about one hour.

Lights Relay

relay air bad low beams

In some models, the problem could be the low or high beam relay. The relays are located in the fuse box in the engine compartment. Replacement automotive relays can be purchased online and easily replaced by any car owner.


If you have the circuit diagram and a digital multimeter, you can do further troubleshooting to diagnose this problem. You should check a few things to determine if the light switch is receiving power. Check if power is being transmitted to the multi-function combination switch.

Switch between the high and the low beam and see if there is continuity at the light and the combination switch terminals. You cannot perform much troubleshooting without a multimeter, so start by getting a Digital Multimeter. If your headlights are not working, you might not be able to see the road. Properly working headlights are critical for your safety.

We hope you find the Why Headlight is Not Working – Bulb OK guide helpful. Check these troubleshooting and repair guides for more help on your vehicle.

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