Why is the brake light only on one side?

The cause could be a faulty brake bulb, or a bad connection in the bulb wiring. Tighten the light bulb by hand and try again. If the light bulb is on, it is the cause of the poor contact of the light bulb; if it is not on, it means that the light bulb is broken and needs to be replaced.

The brake light of the car is the most important signal indicator light in the tail light of the car, and it is also a very important driving equipment. The brake light is a direct signal transmission indicator light for stepping on the brakes. It can mainly warn the surrounding vehicles and effectively prevent accidents. According to the relevant provisions of the "Road Traffic Safety Law", before driving a motor vehicle on the road, the driver should carefully check the safety and technical performance of the motor vehicle to avoid potential safety hazards. The brake lights will also appear to be always on, most likely because the brake light switch is faulty, and there will also be a phenomenon of being off all the time, which may be caused by poor contact of the line, damaged bulbs, and damaged brake switches.