Fog lights are typically mounted low on the front of your vehicle and differ in shape and function from standard headlights. Their main purpose is to improve visibility in challenging weather—like dense fog, heavy rain, or snow—when regular headlights just don’t cut it. When fog lights are not working, it can seriously affect your ability to drive safely in poor conditions. Given their importance, fog lights should be checked and serviced regularly to keep you safe on the road.

In this guide, we’ll walk you through the most common fog light problems, how to identify them, and the steps to fix them if your fog lights are not working.

Common Signs Your Fog Lights Aren’t Working

1. Fog Lights Won’t Turn On

If your fog lights don’t come on—whether manually or automatically—it could be a sign of several issues. This is often the first clue something’s wrong. If both lights fail to activate, it’s best to have your vehicle inspected by a mechanic. Possible causes include a blown fuse, a burned-out bulb, faulty wiring, or a defective relay.

2. Dim or Flickering Lights

Flickering or unusually dim fog lights can be distracting and unsafe. This typically indicates loose wiring connections, a relay that’s starting to fail, or a bulb nearing the end of its life.

3. Blown Fuse

Fuses protect your vehicle’s electrical system from power surges. A blown fuse will cut power to your fog lights entirely. Replacing the fuse is easy, but if it blows again, you might be dealing with an underlying electrical issue that requires professional diagnosis.

4. Faulty Fog Light Relay

The relay controls the electrical current to the fog lights. If it fails, your fog lights may not turn on at all or might stay on even when the switch is off—draining your battery.

Bad Fog Light Bulb Relay

The fog light relay is a critical component in your car’s electrical system that controls the power sent to your fog lights. When the relay malfunctions, it can lead to several problems.

What Does a Fog Light Relay Do?

A relay acts as a switch that allows low-current circuits, like your fog light switch, to control high-current circuits, such as the fog lights themselves. It ensures that the lights operate efficiently without overloading the wiring.

How a Faulty Relay Can Cause Fog Light Issues

Fog Lights Don’t Switch On:

If your fog lights don’t respond at all, the relay could be to blame. The headlight switch might be working fine, but the relay is responsible for delivering power to the fog lamps. If the relay fails, the electrical current can’t reach the lights, leaving you without visibility in fog or heavy rain.

Fog Lights Won’t Turn Off:

Fog lights that stay on even after switching off your headlights could indicate a stuck or shorted relay. When the relay fails in the "closed" position, it keeps supplying power to the fog lamps continuously. This not only drains your battery but may also damage the lighting system if left unresolved.

If you suspect the relay is the issue and want to replace it, check your vehicle’s manual to locate the relay box, usually found under the hood or near the dashboard, and swap the faulty relay with a new one.

Steps to Diagnosing Fog Lights Problem

Tools & Supplies You’ll Need

You’ll need replacement fog light bulbs (LED or standard; ensure correct size), screwdrivers and pliers, a multimeter or power probe, a replacement relay, electrical connectors and wire (if repairs are needed), and some basic knowledge of car wiring.

Step 1: Visual Inspection

Check the fog light switch by turning it on. If nothing happens, go further. Remove and examine the bulbs. If one appears burnt out, replace it. Some aftermarket LED bulbs may not fit your housing—always check sizing.

Step 2: Replace the Bulbs

Install the new bulbs, ensuring the orientation matches the housing. Secure the bulb and reconnect the wiring. Test the switch again. If lights still fail, move to electrical testing.

Step 3: Test Power, Grounds, and Fuses

Locate the relay and fuse, usually under the hood or near the dash. Use a multimeter to check both sides of the fuse. If there’s no voltage, the circuit isn’t live. If available, test with a known working relay.

Relay pin guide: Pin 30 is power from the battery, Pin 85 is ground, Pin 86 is switched power from the fog light switch, and Pin 87 is power to the lights.

Step 4: Inspect the Switch and Wiring

Check if the fog light switch is sending power. For rocker switches (common in aftermarket setups), Pin 1 is ground, Pin 2 is illumination (from dash lights), and Pin 3 is switched power to relay. A common error is using the illumination wire as a power source—it won’t carry enough current.

Step 5: Final Test & Reassembly

Reconnect all components. Turn on the headlights and then the fog lights. Check if the fog lights illuminate and the switch backlight functions properly. If something still isn’t working, recheck all grounds and verify voltage is reaching the fog lights.

Here’s a Quick Troubleshooting Checklist:

Are both bulbs working and the correct type?

Is voltage present at the fuse and relay?

Is the relay functioning?

Is the switch wired correctly?

Are the ground connections clean and secure? Is power reaching the lights themselves?

Frequently Asked Questions

1. Why do my fog lights work sometimes but not always?
Loose wiring or a corroded connector is often to blame. Also check the relay.

2. Can I upgrade my fog lights to LED?
Yes—just make sure they fit and are road-legal in your area.

3. How much does it cost to fix fog lights?
Bulbs typically cost $10–$30, fuses or relays $5–20, and wiring repair $100 or more depending on complexity.

4. Are fog lights required for inspection?
This depends on your local laws. If your car came with fog lights, they often need to work to pass inspection.

5. Can I install aftermarket fog lights myself?
Yes, with basic tools and a little wiring knowledge. Always follow the instructions and seal all connections.

Final Thoughts

Fog lights are an essential safety feature, especially in poor weather conditions. Whether you’re dealing with a blown fuse, a faulty relay, or planning to install aftermarket lights, this guide provides the steps you need to address the issue effectively.

For high-quality fog light bulb replacements and upgrades, consider trusted automotive lighting brands like SEALIGHT. By ensuring your fog lights are in top condition, you can drive safely and confidently, no matter the weather.