How to Fix Dim, Foggy or Burned-Out Headlights

When the clocks fall back in early November, a lot of commutes suddenly happen in the dark. That’s when weak headlights become obvious: a yellowed lens, a dim bulb or one light pointing at the treetops. Most headlight problems fall into a few categories, and many are easy to fix at home. This guide walks through the common causes and what to do about each one.

First, figure out what’s wrong

Park facing a garage door or wall at night and switch the headlights on, first on low beam and then on high beam. Look for:

• One light out completely: usually a burned-out bulb, sometimes a blown fuse or bad connector.
• Both lights dim or yellowish: cloudy lenses, aging bulbs or a charging problem.
• Flickering: a loose connector, corroded ground or failing bulb.
• Uneven beams: headlights out of alignment, often after a bump or a bulb change.
• Condensation inside the lens: a cracked housing or failed seal.

Fixing cloudy or yellowed headlight lenses

Most modern headlight lenses are polycarbonate plastic with a factory UV coating. Over the years, sunlight breaks the coating down and the lens turns hazy and yellow, which scatters light and cuts how far you can see.

How to restore headlight lenses

1. Wash and dry the lens thoroughly.
2. Mask off the paint around the headlight with painter’s tape.
3. Wet-sand the lens, starting with a coarser grit to remove the oxidized layer and working up to finer grits until the surface is evenly smooth and frosted. Keep the surface wet.
4. Polish with a plastic polish or compound until the lens is clear.
5. Seal it with a UV-protective clear coat or sealant. This is the step people skip, and it’s the reason many restorations go yellow again within months.

Headlight restoration kits bundle the sandpaper, polish and sealant together. If the lens is cracked, crazed on the inside or full of moisture, restoration won’t help and the housing needs replacing.

Replacing a burned-out bulb

Find the right bulb

Your owner’s manual lists the bulb size for low beams, high beams and fog lights. Common sizes include H11, H7, H4 and 9005, but cars vary, so check before you buy.

Swap it out

1. Turn off the lights and engine, and let a recently used bulb cool.
2. Open the hood and find the back of the headlight housing. On some cars you’ll need to go through the wheel well or remove a cover.
3. Unplug the connector, twist or unclip the old bulb and pull it out.
4. Fit the new bulb without touching the glass. Oils from your skin can create hot spots that shorten a halogen bulb’s life.
5. Reconnect, test and refit any covers.

It’s worth replacing bulbs in pairs. The other one is usually close to the end of its life too, and a matched pair gives even color and brightness.

Good light makes the job easier

Working behind a headlight in a dark engine bay is much easier with a hands-free light. A rechargeable LED work lamp lets you see the clips and connectors clearly.

Thinking about LED bulbs?

LED bulbs are popular because they draw less power, last a long time and give a whiter light. LED replacement bulbs are sold in common fittings such as H4, H7, H11, 9005 and 9006, so check which one your car takes before you buy.

Before you switch, know the trade-offs:

• Check your local rules. Headlights designed for halogen bulbs aren’t always approved for LED replacement bulbs, so check what’s road-legal where you live. LED bulbs are often sold for off-road or fog light use for this reason.
• Housing design matters. Reflectors and projectors are shaped for a specific light source. A poorly matched bulb can scatter light and dazzle oncoming drivers.
• Aim after installing. Always check alignment after any bulb change.
• Watch for warning lights. Some cars detect the lower power draw of LEDs as a “bulb out” fault.

Electrical problems: fuses, connectors and grounds

If a new bulb doesn’t light, check the fuse for that circuit. The fuse box diagram is usually on the cover or in the owner’s manual. Next, look at the connector behind the bulb: melted plastic, green corrosion or loose pins can cause flickering or a dead light. A poor ground connection can also make lights dim or flicker. If both headlights are dim and the dash lights dim at idle, have the battery and alternator tested, because the problem may be the charging system rather than the lights. Our guide to using a car battery charger covers battery basics.

How to check headlight aim

1. Park on level ground about 25 feet from a wall or garage door, with normal tire pressure and a typical load.
2. Turn on the low beams and note where the brightest part of each beam hits the wall.
3. The beams should be level with each other, with the top of the bright area at or slightly below the height of the headlight centers.
4. If they’re uneven, find the adjusting screws on the housing and make small adjustments, or have a shop aim them.

Your owner’s manual may list a specific procedure, so check it first.

Headlight maintenance for winter

• Wipe road salt and grime off the lenses regularly; dirty lenses block a surprising amount of light.
• Keep a microfiber cloth in the car for quick cleans.
• Check all exterior lights once a month.

Headlights are on our winter prep checklist in car accessories for winter, and a full car detailing routine is a good time to restore hazy lenses.

FAQ

Why is only one headlight out?

Usually it’s just the bulb. Bulbs rarely fail at the same time, which is why replacing both is a good idea.

Does toothpaste fix foggy headlights?

It can polish away a little haze temporarily, but without sanding and a UV sealant the yellowing comes back quickly.