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HomeTips & GuidesLow Beam Relay: Should It Be Blamed For Malfunction Low-Beam Headlights

Low Beam Relay: Should It Be Blamed For Malfunction Low-Beam Headlights

About Low Beam Relay, It’s safe to assume that nobody wants to drive around at night with bad headlights or headlights that don’t completely function. 

Often your high-beam headlights will still function even if your normal headlights don’t. 

However, driving around at night with only your high-beam headlights is unsafe for your fellow drivers as you could potentially blind them.

Headlight systems are often standard and comprise the following components; switch, fuse, relay, and bulbs. 

If any of the components malfunctions, your headlights could stop functioning. Determining why your headlights aren’t functioning will help you determine the best solution. 

The article below will discuss the various situations where your low beam relay is to blame for your headlights not functioning.

Table of Contents

What Does a Headlight Low Beam Relay Light Do?

Basically, a relay is an electromagnetic switch using low currents to control a circuit with higher currents. 

Also, most auto relays are usually open; therefore, the current doesn’t flow between contacts until you activate the relay.

In standard computer-controlled headlights, there are two relays – the first for high beams and the other for low beams. 

Also, some vehicles have a third relay in charge of activating the daylight lights that automatically turn on as you drive during the day.

Upon requesting low beam activation through your headlight switch, there’s a signal sent to the computer (commonly known as the BCM). 

In response, the BCM supplies the ground for a coil in the relay, resulting in current flowing through the coil and creating a magnetic field that closes the relay contacts. 

Then, current flows through your contacts to your headlight assembly in order to turn on the low-beam lights. 

Also, there are headlight systems designed with a relay for switching power between high-beam and low-beam headlights. 

Upon the relay malfunctioning, the power supply could reach your high-beam headlights but not your low-beam headlights.

Furthermore, not every computer-controlled headlight system uses relays. Also, older headlight systems that aren’t computer-controlled don’t use headlight relays. In such systems, the current flows straight to the headlight from the headlight switch via the dimmer switch.

A typical relay wiring diagram

Caption: A typical relay wiring diagram

What are the Symptoms of a Bad Headlight Low Beam Relay?

Once you have a faulty headlight relay, you’ll likely notice the following symptoms.

Low Beam Headlights Don’t Turn On

Normally, your headlight relay will fail in an open position, thus preventing any voltage from getting to your headlights. 

Upon failure of your low-beam relay, the low-beam headlights will not function. 

Similarly, once the relay for the high beam fails, your low beam headlights will not function. Also, if the daylight malfunctions, the daytime lights won’t function.

Low Beam Headlights Won’t Turn Off

Although such scenarios are rare, there are instances where a faulty relay switch can completely close, preventing your headlights from turning off.

Concealed Headlights Don’t Work Properly

Some vehicles, especially sports vehicles, contain concealed headlights that, upon activation, pop up.

 Modern cars with concealed headlights that are computer-operated rely on the relay for activation. 

Therefore, if the relay fails in an open position, your concealed headlights won’t rise.

Many Other Ways That Low Beam Headlights Can Fail

If your low-beam headlights stop functioning, it’s normally an electrical or physical problem. Apart from issues with the relay, some other potential problems include;

Headlight Switch

Most cars contain lever switches on their steering columns that control low or high beams. The switch is designed for regular use; however, it eventually wears out. 

If your problem is the switch, you will probably notice it feels a bit loose or it no longer clicks in position as it previously did. 

If you’re unsure, it’s best to visit a professional mechanic and have them give you the correct diagnosis.

Headlight Switch on Car Dashboard

Caption: Headlight Switch on Car Dashboard

Low-beam Headlight Sockets

Most headlights on cars have bulbs connected to sockets. As time moves, the sockets could corrode, which could be a result of improper grounding or various other reasons. 

Also, some cars have the headlights wired; therefore if one of the light shoes out, so does the other.

However, because the high beam lights use a different circuit, often they would be fully functioning even if the low beam lights are experiencing some issues.

Low-beam Headlight Wiring

Whether you have a loose connection or rodents have chewed the wiring harnesses, your headlights might stop functioning. 

You can use a voltmeter to check the power at your headlights in order to determine if there are any problems preventing power from getting to your headlights.

Automotive Wiring Chewed By Rodent

Caption: Automotive Wiring Chewed By Rodent

Low-beam Headlight Fuse

Every electrical system in your vehicle, including the headlights, is protected by a fuse. If the headlight fuse blows, it could result in your headlights not functioning.

Low-beam Headlight Bulbs

Generally, the normal lights are on more frequently than the high-beam headlights. 

Therefore, they burn out quicker than the high beam headlights. Some cars have separate bulbs for the different beams, while others have headlights with different filaments. 

Regardless, if your high beam lights are still functioning while the high beam lights are still functioning, first check your bulbs.

So, When Should We Blame the Low Beam Relay

Depending on the bulbs that are no longer functioning and the circumstances, you can use the information below to help you pinpoint the exact problem.

One Headlight Doesn’t Work

Cause: Normally, it’s a result of a burned-out bulb.

Fix: Replacing the bulb. If this doesn’t fix the problem, the issue could be with the fuse or wiring.

Tips: HID (high-density headlights) could fail due to other associated components.

Neither of the Headlights Work

Cause: A problem with the grounding or power or burned-out bulbs.

Fix: Check the grounding or power then fix if necessary. Also, you could attempt changing the bulbs.

Tip: Although bulbs don’t normally burn out simultaneously, it’s advisable to still check for power. Most complete headlight failures result from bad components such as the module, fuse, or relay. Also, improper wiring could cause the headlights to stop functioning.

High Beam Headlights Don’t Work, or Low Beam Headlights Don’t Work

Cause: Issues with your headlight switch or relay. However, it could be a burned-out bulb.

Fix: Replace the switch, relay, or bulb.

Tip: If only one bulb stops functioning in either the low-beam or high-beam headlights, the problem could be the bulb. Most headlight issues limited to the low or high beams are related to the relay or high beam control switch.

Headlights Work But Seem Dim

Cause: Charging system problems, foggy lenses, or worn-out bulbs.

Fix: Repair your charging, clean your lenses, or replace your bulbs.

Tip: If the headlights always appear dim, the cause could be worn-out bulbs or foggy lenses. However, if the headlights appear dim under certain circumstances, there could be a problem with your charging system. Some headlight issues could result from a combination of problems, such as improper wiring, bad switches, bad bulbs, and relay issues.

How to Test a Headlight Relay

The simplest method of testing headlight relays is temporarily swapping your current relay with another one in the distribution box

For instance, you could swap your headlight relay with your air conditioning relay if they have the same design. 

And if your headlights function with the alternate relay in place, you know you need to replace your headlight relay.

Generally, you’ll find your headlight relay in the power distribution box inside the engine compartment. If you’re unsure, you can always check your car’s manual.


Now you know that when your low-beam lights aren’t functioning, but high-beam lights work, it’s most likely that there is something wrong with your low-beam relay.

 If you want to replace your current headlight relay, you can rely on Cloom Tech for custom high quality automotive harnesses.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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