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Test Light with Multimeter: The Key Steps

How do you test light with a multimeter? Find out more details on this from this article. Fixing a new car light calls for you to take measures to check if it is working. The best way to test is to use the multimeter. 

The tool is critical in identifying where there’s an electric current issue in an electric circuit. It doesn’t just apply to testing light fixtures but also to other car electronics.

Hence, knowing how to use it ensures you can apply it in many other applications.

Check out the details of how it works below. 

Table of Contents

How to Test a Light Fixture with a Multimeter

A multimeter is the right tool for voltage testing of your light fixtures. It has a wide range of applications, and using it is straightforward. Also, it is the fundamental tool in all electrical repairs. 

Testing with a multimeter involves checking for voltage in the electrical circuit. 

Should You Test a Light Fixture?

A Car Headlight. 

A Car Headlight. 

Sometimes, the light may not work normally, and you could think the issue is the light itself or the circuit breaker. However, the fixture is sometimes to blame, so you should test it to ascertain that it is not the problem. 

Remember that the fixture is at the end of the lighting process. Hence, if it is damaged or not working properly, it affects the entire lighting system. Below, we’ll illustrate how to test a light fixture in detail. 

Test Light Fixture by Checking Voltage

Testing a fixture with a multimeter. 

Testing a fixture with a multimeter. 

A multimeter is among the most versatile electronic tools capable of testing various features. It can test the voltage drop, current, and resistance, commonly referred to as a volt-ohm-milliampere.

Notably, it can test either alternating current voltage or direct current voltage. The former is your home’s electrical wiring current, while your car battery supplies DC current. Here are the testing steps: 

  • Begin by setting up the voltage range; ideally, we use 200V to test household digital circuit fixtures. The aim of using this range is to achieve the 120V, which is the household circuits range. 
  • Next, you should select either to use AC or DC mode. As highlighted earlier, set the device to AC if you’re testing household fixtures but to DC for your car’s lights. 
  • Now configure your multimeter to ready it for testing. The multimeter’s black lead connects to the common port, while the red one connects to the mAVΩ port. 
  • Remove the light from the fixture to start the testing process. Now activate the power breaker and connect the terminals of the multimeter to the light fixture. 
  • Ideally, you should obtain a reading of 120V. But a lower reading so far away from this standard, such as 100V, means the fixture has an issue. 

Test Light Fixture by Checking Continuity Test

A Non-contact voltage tester/ quality multimeter. 

A Non-contact voltage tester/ quality multimeter. 

After checking the electrical voltage, the next most important process is the continuity test. It is handy in finding the resistance between the light fixture connectors. 

  • Start by turning off the power breaker/battery voltage. For home light fixtures, ensure you’re standing on a safe ground, especially if you’re testing overhead lights. 
  • Next, unplug the light fixture to commence the testing process. At this step, also confirm that the light is not the issue. If it’s okay, you can test the light fixture. 
  • Attach the multimeter terminals to the electric power cables and check for current flow. 
  • Finally, test the light fixture. If the multimeter gives a reading, the fixture is okay, but if it doesn’t, it has an issue and should be replaced. 

How to Test LED Light with a Multimeter

A Mechanic Replaces an LED headlight. 

A Mechanic Replaces an LED headlight. 

You require a digital multimeter to test if the LED lights are in good working condition.

  • Plug the red and black leads onto the multimeter. Ensure you connect the black lead (negative terminal) to the ‘COM’ part on the multimeter and the red one of the other terminal. 
  • Set up the multimeter to the diode setting. Remember, unlike incandescent bulbs, your LED is a diode that emits light. So, you must have the multimeter in diode mode for a reading. Setting this up involves turning the dial clockwise until it reaches the part labeled ‘diode.’ 
  • The LED has an anode (the longer prong) and a cathode (the shorter prong). Connect the multimeter’s black lead to the cathode and the red to the anode. Most importantly, the LED’s anode and the cathode shouldn’t touch each other while you’re taking the reading. 
  • When you connect the multimeter’s leads to the LED’s prongs, the LED should light up. 
  • Now, check out the reading on the multimeter’s display. A reading of around 1600 mV shows that the LED is in good condition. 
  • If there’s no reading in the multimeter, there’s probably a problem with your connections. Confirm that you connected the black probe to the shorter LED prong and the red one to the other. Also, ensure that no part is touching the other (the prongs shouldn’t touch as well as the multimeter’s leads). 
  • But if you’re sure everything about the connection is perfect, then the LED is probably the issue. Check out the supply voltage. You’ll have to replace the transformer if the output voltage is insufficient. But you need a new LED if the supply voltage is okay and the LED still doesn’t light up. 

Evaluating the LED Brightness

If everything about your connection is okay, your LED should light up, and the reading should be close to the 1600 mV range. But you need to be keener on its brightness to establish if it’s a high or low-quality light bulb. 

Take the case of an LED with a normal reading on the multimeter, but it’s dim. The inference is that this is a low-quality light bulb. But if it’s a high-efficiency LED light, it should shine bright. 

How to Test a Light Switch With a Multimeter

A Car's Light Switch. 

A Car’s Light Switch. 

Testing a light switch is simple and similar to the processes we have covered above. Let’s look at it in detail. 

  • Start by turning the dial selector by setting your multimeter to the resistance (ohms) mode. Next, turn off the power supply to the light switch you are setting. As a precautionary measure, ensure there’s no residual voltage before commencing the test process. 
  • Now disconnect the light switch from the wall and lay it on a non-conducting surface. You can use something like cardboard or a rubber mat. 
  • Place the multimeter leads on one of the light switch screws and check out the reading of each one. The ideal reading should be close to zero if everything is working appropriately. But the light switch is faulty if you obtain a relatively high or no resistance. 
  • Replace a faulty light switch with a similar one. Ensure the now matches the amperage rating of the wiring box and switch box. After replacement, reattach everything and test again to confirm everything is okay. 
  • Also important is to ensure no electrical contacts are arcing as if present; this could indicate a significantly huge underlying problem. 

The most important bit during this test process is ensuring you’re safe from electric shock. So, before everything, the cardinal safety measure should be switching off power at the electrical panel to avert the shock hazard. 


Lighting is crucial in automobiles and homes, ensuring things run well at night. Therefore, many people spend hundreds of dollars to live in a well-lit environment. But replacing lights can also be expensive. 

Hence,  you need to be sure they’re faulty before buying new ones. And testing for faulty lights is key before replacing them. 

We’ve highlighted the various critical processes when replacing light fixtures. With this knowledge, you can now test all lights without involving a technician. 

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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