The fog light relay is the electrical relay that is responsible for controlling power to the fog lights. The fog lights are lights underneath the headlights that are designed to improve visibility in dense fog or rain conditions. They are meant to help the driver see the edges of the road when visibility is low. When the fog light relay fails or has any issues, it can cause problems with the operation of the fog lights. Usually a bad or failing relay will produce a few symptoms that can alert the driver of a potential issue.
1. Clicking sound from the relay
One of the first symptoms of a problem with the fog light relay is an audible clicking noise from the relay. Many relays will produce a quiet audible click when they are switched on, however, an excessively loud click may be an indicator that the relay may be having internal issues.
2. Fog lights are always on
Fog lights that remain on at all times are another symptom of a problem with the fog light relay. If the fog light relay shorts internally or has any wiring issues, it can cause the fog lights to remain on at all times. This is obviously an issue, as it will drain the battery of the vehicle as well as significantly shorten the life of the bulbs.
3. Fog lights do not turn on
Another common symptom of a faulty fog light relay are fog lights that do not come on at all. The fog light relay is the switch that controls power to the fog lights, and it is usually controlled either automatically by the computer or manually by the driver. If the relay fails, it will disable the power to the fog lights and render them inoperable.
While fog lights are not typically used in normal driving conditions, they are useful to have in low visibility conditions, such as during heavy rain or dense fog. If you suspect that your fog lights, or relays, may be having an issue, have the vehicle inspected by a professional technician, such as one from YourMechanic, to determine if the car needs a fog light relay replacement.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Fog Light Relay and was authored by Eduardo Ruelas.