How and Why Ford F-250 Super Duty Fog Lights Go Bad
While they aren't very useful in clear weather, fog lights are extremely handy in situations where heavy precipitation or other road conditions make it difficult to see past your hood. By helping your eyes find the edges of the road, the lane markings, and generally lighting up the ground ahead, these specialized lights help you avoid disaster that could cost you your truck--or even your life. Inevitably, however, wear and tear will cause problems. Here are some examples of how fog lights malfunction and why:
Puddles of water and other signs of exessive condensation
Large amounts of moisture can result in rusted connections and, in the worst case, exploded bulbs. The exterior lamps on your F-250 truck are vented to allow for normal changes in pressure. A side-effect of this is that moist air can enter the assembly through the vent, which can form as mist on the interior. Thin, fine mist is fine and will eventually disappear by itself. Watch out for large water droplets, drip marks, and puddles inside the lamp. The probable cause is a plugged vent. Most vents can be found near the bottom-rear of the fog light assembly. Some fog lights have a blue material that acts as a kind of filter for the vent. It may help to remove the filter altogether.
Dim or non-functional lighting
It's always a good idea to check the bulb first. Carefully disconnect the fog light bulb and test it with a 12 volt source, such as your car battery. If the light is dim or it doesn't light at all, then you've found your culprit. If it works fine, then the problem likely lies in a poor circuit connection or a bad fog light switch. Check the wiring for anything loose or corroded. Also check for voltage continuity using a test light (with your owner's guide as a reference). If the connections are good, have a look at the switch. The bezel that holds the headlight rotary switch can be pulled right out of the panel which allows for easy tinkering with the circuit board. There, you can check if the spring-loaded rotary switch is dirty or stuck.