Some cars may differ, but most headlights have fuses for each individual headlamp. If your headlights are functional on the low-beam setting, but won’t switch to high beams, the first thing a mechanic will check is the fuse. The second thing to check is the headlamp bulb. The mechanic can replace a high beam with a new bulb. If that doesn’t work, it’s most likely that the relay that switches the system to high-beam supply has failed. If it isn’t bulb trouble or relay failure, the problem may reside in the light switch itself. To check that component, a multimeter and a wire-piercing probe are essential aids, and the mechanic will refer to your car’s wiring diagram. For steering column-mounted lightswitches, where wiring for the car’s airbag is also routed through the column, it may be necessary to remove the steering wheel to replace the switch.