Why is one rear fog light on and the other off?
3 Answers
The reason why one rear fog light is on and the other is off is that there is only one rear fog light. The main purpose of having only one rear fog light is to distinguish it from the brake light. Below are specific details about fog lights: Types: In addition to the front high beams, low beams, headlights, and parking lights, as well as the rear running lights and brake lights, most vehicles also have a set of anti-fog lights installed in inconspicuous locations at the rear. Rear fog lights are red signal lights installed at the rear of the vehicle to make it easier for other road users to detect the vehicle in low-visibility conditions such as fog, snow, rain, or dust. They emit a stronger light intensity than tail lights. Location: Fog lights are mounted at the front of the vehicle, slightly lower than the headlights, and are used to illuminate the road during rainy or foggy weather. Due to reduced visibility in foggy conditions, the driver's line of sight is limited. These lights can increase the visible distance, especially yellow anti-fog lights, which have strong light penetration and can improve visibility for both the driver and other road participants, allowing oncoming vehicles and pedestrians to spot each other from a greater distance.
Last week, my car's rear fog light had the same issue. While driving back to my hometown, I noticed the left one was on but the right one wasn't, almost causing an accident in the fog. At first, I thought the bulb had burned out, as it's normal for bulbs to fail when they reach the end of their lifespan—my car is almost ten years old, so the bulb was due for replacement. However, after checking, I found the bulb was fine, so it might have been a loose wire or a blown fuse. Aging circuits or poor contacts often cause one light to work while the other doesn't, especially with the rear fog light wiring, which is prone to corrosion. I opened the tailgate and checked the connector—sure enough, it was loose. Tightening it fixed the issue. If it had been a short circuit or blown fuse, I would have needed to use a multimeter to check the voltage, as unstable voltage can make the light flicker. If you can't fix it yourself, take it to a repair shop immediately—don't delay, safety comes first. Checking your car lights monthly can save you a lot of trouble and prevent driving nervously at night. Also, using fog lights more often in winter or rainy weather adds peace of mind.
I once encountered the issue of a single rear fog light not working when I tried to fix it myself, which is quite common. First, check if the bulb is burnt out and try replacing it with a new one. If that doesn't work, inspect the wiring—it could be due to insufficient current caused by an open or short circuit. I used a multimeter to check the fuse box near the rear wheels and found that the fuse on the right side had blown. If the socket is dirty or has moisture, it can also cause poor contact, so cleaning it might help. A faulty relay could also be the culprit, as it controls the light's switch, and if it's damaged, the headlight switch might be affected. Voltage fluctuations are another factor, as unstable alternator output can damage the circuit. If you're planning to DIY, there are plenty of video tutorials online, and spare parts aren't expensive. Remember to wear insulated gloves to prevent electric shocks. After fixing it, take a photo with your phone to verify both sides are working before test-driving. This issue is easy to overlook but affects nighttime visibility, so I recommend a comprehensive inspection of the lighting system every six months to prevent accumulated faults.
