What is the dome light bulb? The fog light relay acts as a switch that controls when the fog lights are activate? depending on certain criteria. Typically the fog lights will not come on if the headlights are not on or if the headlights are on high beam in some vehicles. The relay directs power to the fog lights only when the switch is on and the right lighting circuits are on. How do you know your fog light relay needs to be replaced? You hear a clicking sound when you attempt to turn the fog lights on Fog lights do not work and the appropriate switches dont light up Fog lights will not switch off How is the fog light relay replaced by a mobile mechanic? The faulty fog light relay is identified and access panel removed. The broken fog light relay is removed and a new one is installed. The fog lights are tested for proper operation and access panel is installed. How important is is it to have your fog light relay replaced? All lights on a vehicle are required to be functional in order for your vehicle to be considered safely operational. If your fog lights are not workin? your vision may become obstructed in situations where you need to use these lights.