Car Headlights Not Working – How to Tell If Your Headlights Are Faulty

Car headlights that fail are an enormous safety risk; driving without them should never be attempted. Luckily, most issues can be remedied quickly with just a simple check.

Your headlights rely on several basic components, including fuses, relays and switches to function effectively. In this article we’ll address some of the most frequently experienced issues related to them.


If one headlight is not functioning, it could be that its bulb has burnt out – this is common, however it could also indicate that there’s something amiss with either your headlight relay or high-beam control switch.

Before replacing any fuse that supplies power to headlights, first confirm whether or not its fuse has blown. If it has, replace it with one having an equivalent amperage rating; using higher ampere ratings could potentially cause serious electrical damage.

Headlight switches located on dashboards or steering columns control a relay inside of fuse boxes that controls power to the headlights on and off. Should your solenoid in the relay be compromised, swapping out with one from another part of your car may help solve it; alternatively, your local YourMechanic technician can inspect both headlight relay and wiring and perform any necessary repair as soon as possible.


When both headlights stop functioning, usually there is either a wiring or electrical problem. Rodents could have chewed through a wire, or perhaps the headlight relay that prevents surge current has stopped working – or perhaps its activator switch has stopped receiving signals to trigger it.

Simply replace the fuse with one that has the same amperage rating; if that doesn’t solve the issue, headlight relay or ignitor module replacement might be required.

Since the headlight relay activates both low and high beams, it could be that either one or both beams have become disabled, or that its switch has become damaged. Diagnosing this problem may require using a voltage meter; otherwise if no power is flowing to the relay when activated by switch it may need replacing or the wiring between relay and switch may need checking for continuity.


If only one headlight setting, like high or low beam, stops working while others continue working normally, it could be indicative of a failed relay. Replacing one is typically an easy DIY repair solution and usually costs under $30.

Many cars feature relays for each of their two headlight settings. Unfortunately, headlight relays may develop issues, including failing to turn on or shut off lights while leaving one headlight setting untouched.

When installing a headlight relay, it is vital that it is placed in an effective location. Relays should be mounted as close to both the battery and existing headlight wires as possible for optimal functioning. Also ensure a large gauge wire feeds your relays – especially if using Japanese vehicles with ground-switched circuits.


Your car’s headlights rely on its wiring system to obtain power and shine brightly, but if one of the ground wires becomes damaged, electricity won’t flow into them and they will remain off. Corrosion or rodent chewing through can cause this problem as well; to resolve these issues you will require professional assistance.

Once the switch for your headlights is activated, it sends a signal to turn on a relay that supplies power to low and high beam headlights. Before switching them on again, inspect this relay for signs of damage such as discolored terminals.

If the fuse for your headlight circuit has blown out, replace it with one with the same amperage rating – anything higher may cause irreparable harm to its electrical system.