Mercedes-Benz S350 Rear Fog Light Only Lights Up on One Side
3 Answers
In EU regulations, there is a little-known stipulation that if a vehicle is equipped with two rear fog lights, they must be positioned at least 10 centimeters away from the brake lights. However, this regulation doesn't seem to be enforced domestically. The reason for this distance requirement is that when rear fog lights are too close to the brake lights, following vehicles may easily confuse the two, interpreting the illumination of both lights as the preceding vehicle braking, which could potentially lead to traffic accidents. On the other hand, there's a rationale behind having only one rear fog light illuminated. It helps following vehicles better distinguish between the rear fog light and the brake light. Moreover, using just one rear fog light often enhances the attention of drivers behind, making it easier for other vehicles to notice the preceding car. As for why it's the left rear fog light that's typically illuminated rather than the right one, in China, where traffic keeps to the right, the driver sits on the left side.
Last time at the repair shop, I encountered a Mercedes-Benz S350 with only one rear fog light working—the left side. This is actually common in luxury cars due to their meticulous design. Regulations permit installing the rear fog light only on the left to prevent confusion with brake lights in foggy conditions. If you notice the right side isn’t lit, first check the manufacturer’s design—refer to the manual’s diagram for clarity. Of course, it could also be a genuine fault, like a burnt-out bulb or oxidized wiring on the right side. I once fixed a case where water seeped into the connector during car washing, causing a single-side failure. If it’s by design, don’t overcomplicate things. But if both sides used to work, visit a professional shop to inspect the taillight housing, fuses, and wiring harness. Mercedes wiring is complex—tampering without expertise might short-circuit the turn signal module.
When driving my friend's S350 on a long trip, I noticed that only the left rear fog light was on, so I specifically consulted a 4S technician. Luxury cars usually only have a single rear fog light installed, which complies with regulations while avoiding dazzling the drivers behind with strong light. If your car only has the right side lit or doesn't respond at all, it might be a malfunction. Common issues include dust accumulation in the fog light assembly causing poor contact or loose wiring connectors. Especially during the rainy season, it's prone to short circuits due to moisture. I recommend first checking the corresponding 15A fuse in the fuse box, located in the black box under the driver's seat. If the fuse is fine, it's likely the bulb needs replacing. For this Mercedes, replacing a bulb requires removing the entire rear bumper, and doing it yourself can easily scratch the paint.
