Electrical – How to test a three-way switch to determine if it’s working


I have a light fixture in my house that suddenly stopped working. I tried replacing the lightbulb and still non luck so I decided to try and see if it was the three way light switch itself using a multimeter, but I'm having trouble deciphering the results.

From what I understand, I should be able to:

  1. Turn off power to the circuit
  2. take my multimeter and put it in continuity mode
  3. touch the two screws that are on the same side
  4. when I flip the switch back and forth it should alternate between beeping and not.
  5. The same but beeping for the opposite positions when I touch the screw on the other side of the light switch instead of the screw below

When I perform this test, it beeps regardless of the position when I touch the screws that are on the same side and it doesn't beep at all when I touch the screw on the other side. Does this mean that my switch is broken or am I testing incorrectly? If it is broken, wouldn't the light be on all the time instead of not turning on at all?

Another interesting thing that I noticed – all of the screws on the side of the switch were loose. I went ahead and tightened them up, was that the correct thing to do? What effect could the loose screws have on the light?

Images of the switch below:

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Best Answer

1: You have a 3 way switch which has a traveler line. your odds of having a bad 3 way keeping the fixture from not working while possible would mean that both positions [Off and On] of the switch fail, or both switches have failed. Because when one switch is off the other line is working (either of the switches can turn the light on or off.)

2: Measure for voltage at the fixture wires.

  • Turn one switch On and then Off while measuring do you have any voltage ?
  • Turn the other switch On and then Off while measuring do you have any voltage ?

I am going to post a wiring diagram of a 3 way switch lighting circuit so you can see how and where you need to place your leads when checking the switches. I would be measuring VOLTAGE.

3 Way Switch Light Circuit

There has been a comment on using the push terminals on the electrical switch or using the terminal screws - the push is faster and more likely why people use it and also if you have connected runs. Don't hook two wires on one Screw , use the push terminal to make that additional connection.

As for removing wires from the push terminals: I use a 3.5mm Slotted Screw Driver mine is just like the one pictured below and I have no issues with it - of course I am experienced with push terminals and know that you must insert into the release mechanism and apply pressure on the release either by a slight twist of the screw driver (recommended) or using a prying motion to open the release.

3.5mm Red Slotted Screw Driver

You can obtain the tool from here :


I am not endorsing this vendor, I am posting their link because that is where I obtained the picture from. I have no affiliation with them and have never done business with them.