What causes one headlight to be on while the other is off?
2 Answers
One headlight being on while the other is off is due to a blown fuse or a short circuit in the bulb. Here are some maintenance precautions for car headlights: 1. Replacement: Car headlights should maintain good sealing, especially to prevent contamination and damage to the reflector coating. When replacing bulbs and diffuser glass, avoid touching the lens with your fingers to prevent leaving sweat or oil marks that could cause the reflector to lose its luster and reduce reflective efficiency. 2. Regular inspection: Periodically check and adjust the headlight beam to ensure the headlight's illumination distance meets requirements and that the high and low beams are aligned. The diffuser glass should be correctly installed as specified to prevent loosening or displacement and to maintain the vertical alignment of the prism.
Last time I encountered this situation, I went straight to the repair shop. The experienced mechanic took a look after opening it up and said the bulb was burnt out. Turns out the two headlights have independent circuits, so if one side isn't working, the most common cause is a blown bulb. Another frequent reason is a blown fuse—check the fuse box to see if the small fuse corresponding to the headlight is blackened or broken. I've also dealt with poor connector contact, where water accumulation after washing the car caused oxidation and poor connection. A relay issue could also cause one side to fail, similar to a tripped circuit at home. For older cars, it's worth checking if any wiring has been chewed by rodents. You can try replacing the bulb yourself, but for circuit troubleshooting, it's best left to professionals—haphazard wiring can create hazards.
