How to Test a Headlight Bulb with a Multimeter (Guide)

Finding out that your headlight has stopped working while driving out of the garage can be frustrating. It is even more annoying when you have to drive at night.

For most people, the next step is to take the vehicle to the mechanic shop. This is often the first reasonable step when you have a bad bulb. For a start, getting to the bulb is difficult. 

Not only that but fixing it can look like a big task. However, it is easier than you thought. With a multimeter, you can check your headlight bulbs and replace them if they are bad. Now, if the issue is with the car, you should take it to the mechanic to have a look. 

Most times, when the light bulbs stop working, it is often an issue with the bulb. That means you can fix it without a trip to the mechanic. This guide describes how to test a headlight bulb with a multimeter. Let’s get right into the details!

Quick Answer: Testing a headlight bulb with a multimeter is a simple technique. First, retrieve the bulb from your vehicle. Second, put the probes on the multimeter on two sides of the bulb to check for continuity. If there is continuity, the reading on the device will show it. Next, check the connector to be sure that no other issue exists.

Steps to Test a Headlight Bulb with a Multimeter

It is essential to mention that some cars come with a set of spare light bulbs. You can find them in the trunk of your vehicle. If your vehicle did not come with a set, you can buy a set of new ones from the store.

It is recommended that you have at least a set in your car for easy replacement when a bulb goes bad. A set of new bulbs can cost anything between eight to one hundred and fifty dollars. The actual cost will depend on your car type and the output socket, among others.

Now, let’s get right down to the actual checking of the car light bulb. Here is how to test the LED headlight bulb with a multimeter. (1)

Step 1: Retrieving the Bulb

This is where you need a digital multimeter. You do not need to get an expensive device to get the job done. The first thing to do here is to remove the glass or plastic cover on the vehicle. This is to get to the bulb. After removing the cover, carefully unscrew the bulb to remove it from the socket.

Step 2: Setting Your Multimeter Up

Pick your multimeter and set it to continuity mode. You can also set it to 200 ohms, depending on the type of device you have. It is easy to verify if you have set the multimeter correctly to the continuity mode. To do this, press the probes together and listen for a beeping sound. If it is set to the continuity mode correctly, it will generate the sound.

The next thing is to locate your base number. You will need to back-check the figures you get with the base number with the actual one you get after checking the car lightbulb. This will let you know if your bulbs are still working or not. 

Step 3: Placing the Probes

Next, place the black probe in the negative area of the bulb. Put the red probe against the positive pole and press it for a moment. If the bulb is working perfectly, you will hear a beeping sound from the multimeter. You would not hear any sound if the bulb switch is broken because there is no continuity.

You can also check if your bulb is good or not by checking its physical appearance. If you can see black marks on the inside of the bulb, it means that it is broken. However, if you do not see any sign of damage caused by cracking or overloading, then the issue may be more related to internal damage. That is why you need to test it using a digital multimeter.

Step 3: Understanding Your Reading

If you have a bad bulb, no reading would show on the digital multimeter, even if the bulb looks good physically. That is because there is no loop. If the bulb is good, it will show a reading close to the baseline that you had earlier. For instance, if the baseline is 02.8, a good bulb should be within the range of the reading.

It is worth mentioning that the type of bulb your vehicle uses will also determine the reading. For instance, if you use an incandescent bulb, if it reads above zero, it means the bulb is still working. However, if it reads zero, it means the bulb needs replacement.

If your headlight bulb is fluorescent, a reading that 0.5 to 1.2 ohms mean that continuity exists in the bulb and it should be working. However, if it reads below the minimum, it means it is bad and needs replacement.

It is worth mentioning that a successful reading does not mean that the bulb is working well. Therefore, if your light bulb is not working even when the digital multimeter shows that it is in perfect shape, you should visit your local mechanic shop to have an expert take a look.

Step 4: Checking the Connector

The next step is to check to see if the connector is good. The first step is to pull off the connector around the back of the bulb from the car. You should be careful when pulling off the connector so you do not pull off the wire from the connector. (2)

There are two sides to the connector. Put the probe on one side of the connector. If you use a base voltage of 12VDC, you can set it at 20VDC on the digital multimeter. Next, go into the car cabin and turn on the headlight to see the reading.

The reading should be as close to the base voltage as possible. If it is very low, it means the connector has an issue. If the connector is good, then it is the bulb or bulb switch that has an issue. You can change the bulb or fix the switch issue to resolve the issue.

It may interest you to know that you can do this on other bulbs. You can test your household bulbs that are no longer working. The principles are the same, even though you may see some variances in the output.

You can also use this method to test your Christmas lights, microwave, and every other household item. If there is continuity, the multimeter will produce a sound or light signal.

Wrapping Up

With these simple steps, you can check your headlight bulbs and fix any issues with them. If the issue is with the bulb, it is something you can fix by yourself. All you have to do is get a new bulb and replace it and your headlight will come back to life.

However, if it is a mechanical fault, such as a problem that has to do with the switch or connector, you may have to visit a mechanic.

Take a look at some of our related articles below.




References
(1) LED – https://www.lifehack.org/533944/top-8-benefits-using-led-lights
(2) car – https://www.caranddriver.com/shopping-advice/g26100588/car-types/

Video Reference

About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gI realized early on carpentry was a huge passion for me and I’ve stayed in the industry for over 20 years now. This gives me a unique ability to really be able to tell you what the best tools and recommendations are. I’m not only a carpenter but I also like machinery and anything to do with electrics. One of my career paths starting off was as an apprentice electrician so I also have a lot of experience with electrical products and anything related.