Fogged headlights create an obstruction in the lens. The fogging will absorb and scatter the light beam produced by the headlamp. Headlight fogging can occur from damage to the exterior lens or condensation on the interior headlight. Interior condensation results from water being introduced to the headlight by way of cracks, leaks, or inadequate seals. When the light is not at full strength, night and low light visibility is reduced. During inclement weather this may create a safety hazard.
Shine a light through the headlight at an angle to determine if the fogging is a result of condensation or particles on the interior surface. If so, there is likely a crack or seal problem.
Remove the headlight. While each vehicle will have different instructions, there usually there are two or three bolts or screws which hold the headlight in place. Once those are removed, the headlight can be pulled forward for inspection. If the bulb can be removed, do so by twisting the bulb casing to release it from the headlight. Sealed beam headlights on older vehicles do not have a bulb which can be removed.
Use a hair dryer to dry the inside of the headlight or, if the headlamp is sealed, use the hair dryer to warm the headlight to dissipate the fogging. If possible, wash and wipe the interior clean. If the bulb was removed, prepare a soapy water solution and pour into the headlight. Swirl the water around and dump. Rinse the interior and either dry with the hair dryer or towel dry. If towel drying is desired, you may have to twist the towel to gain entry to the headlight.
Determine the cause of the leak. Inspect the headlight for cracks or breaks. If a crack or break is found, mix (according to manufacturer instructions) the plastic epoxy and apply along the full length of the crack (both inside and outside the headlight if possible). If the seal around the headlight is damaged, you may need to buy a new headlight. If no visible damage exists, inspect the bulb seal (around the base of the headlight bulb still attached to the vehicle) for deterioration. Replace as necessary, or coat with silicon spray to help ensure a good seal when the bulb is replaced.
Replace the bulb by inserting the bulb into the headlight and twisting to lock in place. Replace the headlight assembly and replace the bolts or screws to secure the headlight.
Wash and clean the headlight with glass cleaner, such as Windex or Glass Plus, which usually contain ammonia. The glass cleaner may remove the oil and any road debris build-up which cause fogging. Use a quality car wax (cleaner car waxes will work best) to restore some lustre to the headlight. If the fogging is removed, no further restoration is necessary, though application of a protectant (Step 3) is recommended.
Use a headlight restoration kit (such as one from Meguire's, Mother's, Diamondite, 3M or other manufacturer), if the glass cleaner and wax do not sufficiently remove the fogging. Restoration kits will contain the necessary products and materials to enable you to remove the outer layer from the headlight to restore clarity. Follow manufacturer's instructions.
Apply a surface protectant, such as a car wax or plastic protectant to the headlight. Restoration kits usually contain a product which protects the outer layer of the headlight from further damage. Car waxes, plastic protectants or products from restoration kits will shield the headlight from UV damage and oxidation. The layer also will provide a buffer between the headlight and any road debris (bugs, tar, oils or other).
Periodically, reapply the car wax, plastic protectant or restoration product to protect the headlight. Reapplication will extend the time the headlight remains undamaged and clear.
Fully sealed headlights with interior fogging may need to be replaced, as moisture may degrade the bulb filaments.