Headlights are among those most important things for night driving and surety of safety on the road. Like all the other components in the car, it can malfunction too. In such a case, where one low-beam headlight is not working, that really is frustrating and might get dangerous because this compromises your visibility and makes you harder to see by other drivers.

Anything from a simple bulb burnout to complex electrical problems may be a reason for one low-beam headlight failing. This article will review the most common failures of a low-beam headlight and discuss some simple diagnoses and repairs.

Burned-Out Bulb

The primary reasons for the failure of a low-beam headlight are a burnt-out bulb. Generally, bulbs in any vehicle are replaced after using them for approximately 500 to 1,000 hours. With time, its internal filament weakens due to continuous use and finally breaks; hence, the bulb becomes ineffective. If only one low-beam headlight is out, first check the bulb on that side.

How to Check:

Open the hood and reach behind the headlight to the headlight bulb housing.

Pull the electrical connector off the back and pull the bulb out of its socket.

Look inside at the filament for any signs of breakage; or more often, the color of the glass looking blackened.

If defective, replace it with a new one of the specification of your vehicle. Though this may seem contrary to common sense, it is recommendable to replace both low-beam bulbs at the same time because the working one may soon stop working since it has been in use almost the same duration.

Read More: Low Beam vs High Beam

Blown Fuse

Most cars have separate fuses for the left and right low-beam headlights. This is so that in case one headlight fails, the other may still work. If your bulb looks perfectly fine, the next place to investigate would be the fuse box. That could also be the culprit of a blown fuse.

How to Check:

First, consult your car's owner manual to find where your fuse box is. They are basically under the dash or under the hood. Find the fuse for your low-beam headlight on the side that isn't working. Using a fuse puller or tweezers, pull it out and inspect if there is a break in the filament inside the fuse.

Change it with another fuse of similar amperage rating if the fuse is blown. Insert the right fuse for your safety and other electrical issues.

Bad Relay

Like with fuses, some vehicles have a separate relay that controls the low-beam headlights. If that goes bad, power won't get to one of the headlights, and it will stop working even if it has a good bulb and fuse. In some vehicles, the headlight relays wear out or go bad and can act intermittently or fail completely.

How to Check:

Find the relay box-usually near the fuse box.

Refer to the vehicle manual for locating the low-beam headlight relay. Replace the relay by an identical replacement, if available for testing whether or not the problem is in the relay. If the swapping of the relays leads to the headlight working, then the problem was with the relay itself and should be replaced.

Wiring Problems

The other more common cause of headlight failure involves wiring problems. Over time, this wiring harness that connects your headlight bulb to the power source will eventually wear down, loosen, or corrode. A break or short in the wiring could prevent the headlight from functioning properly.

How to Check:

Visually inspect the wiring going into the headlight for any signs of damage, corrosion, or loose connections.

Wiggle the connectors to see if the headlight flickers on. If it does, this shows a loose connection.

You can use a multimeter in order to check for continuity in the wiring. Lack of continuity will signal a break in the wiring that has to be either repaired or replaced.

You may also have to solder them back together or use wire connectors if you find the wires damaged.

Faulty Headlight Switch

Other less common causes but possible ones include the following: the headlight switch is faulty. In case the switch operating your headlight is bad, then it does not send the right signal to one of the low-beam headlights. This would be more so expected on older vehicles where the switches can wear out with time.

How to Check:

This would entail the headlight switch check for any inconsistency in the headlamp operations by generally turning them on and off. When possible, check with a multimeter whether the switch is providing correct voltage to the headlight circuit.

If it is bad you will have to replace the headlight switch. Unless you're comfortable with electrical repairs, this may be a job for the professional mechanic since it requires you to tear up part of your vehicle's dashboard in order to do so.

Issues with the Ground Connection

Grounding Each headlight assembly requires an adequate ground to function as it should. The headlight may not work at all if the circuit is grounded poorly, or if the connection is corroded. The problems related to the grounds usually occur inside the areas where water can seep into the connections and begin to rust - that decreases conductivity.

How to Check:

Follow the wire that is attached to the headlight assembly.

Scrape any rust and corrosion off of the ground connection

Using a multimeter, check resistance between the ground wire and a known good ground on the vehicle to test for proper grounding.

Poor Ground Connection- Cleaner or re-secure for proper function.

Conclusion

The causes of malfunctioning low-beam headlights may be due to the bulb that has burned out, blown fuse, faulty relays, wiring problem, defective headlight switch, or poor ground connection. Most of the time, diagnosis and repair start with the simplest solutions, such as checking the bulb and fuse, before resorting to complex electrical checks. You want to maintain your headlights in working order for road safety; thus, you need to address headlight issues immediately. Whatever you cannot figure out, or are unsure of, always consult with a professional mechanic to avoid further complications.