How to Test a Light Switch with a Multimeter

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How to Test a Light Switch with a Multimeter

Switches play a vital role in opening and closing the flow of electricity through an electrical circuit to power a machine with the necessary energy. Therefore, whenever you turn on your light switch, and nothing seems to happen, you need to know that there possibly is an underlying issue. You then need first to check whether your bulb is well-positioned in terms of how well it is screwed as well as whether the bub is still functional. Consequently, make sure that the circuit has the required energy and does not have a blown fuse.

However, if numerous bulbs fail to work appropriately in the same light socket, you should then make use of a multimeter to check if the current is still flowing correctly. This is due to the possibility of having a damaged switch hence the need to use a multimeter to test whether or not it still is functioning as needed.

There are specific essential tools you will need to run the test effectively, and these tools include;

  • A non-contact voltage tester that you will use to examine if the switch and wires have energy before you touch it.
  • Screwdrivers, usually a flat-headed one, and the Philips model used for switch removal as well as disconnection of switch wires.
  • A multimeter is a multipurpose tester that you can use to measure different electrical properties including amperage, resistance as well as voltage. Furthermore, this device can also be useful when carrying out simple continuity tests, and for it to test continuity, the tester dial should be set Ohms or Continuity setting. Typically, any “closed” circuit has continuity, whereas an “open” circuit is broken and does not have continuity. The light switch opens as well close the lighting circuit, and continuity is usually present when it is turned on and absent when it is switched off. Nevertheless, if the light switch has failed, then continuity is not there since the circuit has not been closed.
  • Electrical tape

Steps to testing a light switch using a multimeter

Switch off the power

This is important for own safety reasons by switching off the appropriate breakers in the breaker box, and this will completely turn off all the energy from the switch circuit. If the design of your house is old-fashioned, you then using a fuse panel need to take off the fuse by detaching it entirely from its socket.

Test for any power on the light switch

To do this, you need to remove the screws that are usually placed on the over the switch cover plate so that the wires are fully exposed. Nevertheless, before you even attempt to touch any of the cables, you should first test every wire that is inside the electrical box using a non-contact voltage tester. Additionally, it would help if you did not forget to run tests on the side terminals of the switch. In case this tester notices that there is any voltage, make sure you go back and switch off the appropriate breaker then run the test once more for assurance purposes that there is without a doubt no voltage.

Identify the type of switch

If you want to identify the switch type, you first need to remove the screws on the switch and, with precision, take out the switch from the electrical box. During this process, straighten the wires while noting down the number of side terminals incorporated on the light switch. Furthermore, the light switch has two side terminals, this thus means that this is a single-pole switch.

However, you do not need to count the number of ground screws that typically are green in color, and located either at the top or bottom of the light switch, where it then connects to the green ground wire or bare copper.

In case the switch contains three terminals, you will have to locate a dark-colored terminal and make a label to a wire that is attached to this terminal using an electrical tape. Therefore, this is the terminal that brings power to the switch. Afterward, connect the same wire back to the terminals. The other two terminals are usually unchangeable, so no need for labeling.

Take out the light switch

Loosen both the screw as well as ground terminals and then pull every wire from the terminal. After this, take back your light switch to the work surface where you can now do further testing.

Testing the switch for the continuity

Single-pole switch: With your multimeter, touch all the tester probe to any other screw terminal. After doing this, turn on and off the light switch and when it is on, the reading should be near to zero. Nevertheless, when the light switch is off, the reading shown should be “1” which means no continuity.

Three-way switch: When using a multimeter, you should touch the tester probe to the dark-colored terminal and consequently to the other probe to either of the traveler terminals. Subsequently, turn the multimeter on and off, and the reading should be “1” in one position and zero in the other. After this, shift the second probe to the other traveler terminal, and have the first probe to be common and then do this same test.

Replacing or reconnecting the switch

When you are done, connect your switch as before; tighten the ground terminal as well as the screw terminal firmly. If you are doing a replacement of the previous switch, make use of a new switch that has an identical amperage and voltage ratings that are the same to the original.

Finalize the job

Once you are done with your work, put back the turn the light switch back to its place and then carefully put the wires inside a box as well as using the mounting screws to keep the switch safe. Moreover, fix the cover plate and then switch the switch back the circuit’s power by either reinstalling the fuse or turning on the circuit breaker. Finally, test whether the switch is working correctly.


Having read through this article, you now know the steps you need to follow when testing a light switch with a multimeter. Therefore, whenever you experience any issue, you can easily use this machine to confirm what exactly is the issue without having to hire the services of a professional.

Consequently, you not only save your hard-earned money but also gain valuable skills that you can keep using whenever such an issue arises in the future. Moreover, thanks to the multimeter, it is no longer a hassle to clearly define what the problem is, thereby saving you a lot of valuable time.

About the Author Dan

Just a random guy who likes to build things. Providing tool knowledge, appliance/device testing tips, and DIY project info in an easy-to read & non-intimidating style.