The headlamp switch operates the headlights in a vehicle. It is located on the dashboard and when operated manually by the driver has the option of operating different lights depending on the driving conditions. For example, the fog light option could be used when driving in fog. Often, the headlamp switch also has an option to decide the intensity of the light beam used when driving.
Some vehicles have automatic headlight operation which means that the on board computer decides if lights should be activated depending on the lighting conditions whilst driving. Some vehicles with this option also have a switch to enable the driver to turn the lights out if not needed.
If headlights are failing to light, the first thing to check is the headlight fuses. It may be however that the issue is with a bulb in which case this should be replaced. headlamp switch failures are not uncommon due to the repeated use of this part when driving. Some vehicles will indicate their failure by using a warning light on the dashboard or a warning noise. If a switch fails it should be replaced so lights can be used as normal.