Troubleshooting 3-Way Switches: Why Does My 3-Way Switch Only Work Sometimes?

Troubleshooting a non-working 3-way switch can be a reasonably large pain in the rear for any electrician or electrical contractor. In the latest episode of Electrician U, Dustin gives some tips that will make the process easier.

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So, you have a 3-way switch that only works from one side when the other switch is in one position or the other. In other words, if one switch is in the up position, the other switch will turn the light(s) on and off. But if you flip that other switch to the down position, the light(s) won’t actuate at all. This generally means that you have the travelers crossed and either the incoming hot or the outgoing switch leg on the wrong screws. A relatively easy fix once you can understand how a 3-way works and can visualize the process. PSA- always turn the power OFF before working on any electrical installation!
First, put on your troubleshooting/service electrician hat (figuratively of course!). A good tip- as you are unscrewing the device and pulling it & the wires out of the box, do it gently and slowly. A non-working 3-way may not be a miswiring issue as the source of your power issues but may in fact be loose wiring connections. If you pull something out to fast, you can change the state of the wiring and end up chasing ghosts! When you do get the device/wires pulled out of the box, check the connections on the device to make sure they are nice and tight. When putting switch/wires back in box, be careful not to pinch wires and make sure the bare ground wire doesn't come into contact with any of the screws on the device (with the exception of the green grounding screw of course!).
You may also want to check the wiring colors attached to the different color device screws. 3-way switches have 4 screws. A green one for the ground, a black/dark bronze one for either the incoming hot or the outgoing switch leg, and 2 brass/gold-colored screws for the travelers. Try to keep in mind that you will be bringing IN the power in one switch box and OUT to the fixture in the other box. Either of these locations will generally be done in a single 12-2 or 14-2 cable. The travelers (the wiring going in between the switches) will generally be done in a single 12-3 or 14-3 cable. So, the cable with the single black wire will go to the black screw on the device and the cable with the red and black wires will go to the brass/gold-colored screws. If you happen to see the single black wire attached to a brass-colored screw, then the travelers are crossed and that will generally be the source of your problem!
Depending on length (either the homerun or the traveler length in between the 2 switches) you may have to run the incoming hot and the travelers in #12 but the final switch leg up to the fixtures can be run in #14 (if it is a 15-amp circuit). So, another tip can be to look at wire size. If you look into the switchbox that is being used as the last box before it goes up to the fixture itself, if you see a #14 wire attached to a gold-colored screw, chances are you have something crossed.
In addition to the internal composition of the switches, you may notice that a 3-way switch does NOT have an ON/OFF label on the switch. Due to the alternating nature of the switches and being able to actuate from 2 different locations, they will change position each time you go in/out of different doors.

[FSAUDIOGUY]

That has to be the best trouble shooting explanation of 3 way switch on the internet. Your teaching ability is superior. Thank you for sharing your knowledge.

[sambulate]

Funnily enough, when I asked my wiring instructor for lessons in troubleshooting, this is what he came up with! It would be awesome if you could do more videos on troubleshooting, as that is not something that has been a priority in my residential wiring classes. I'm especially interested in how basic stuff, and in how we'd go about finding and repairing problems in old houses, but anything would help.

[mbmb]

You gave me everything I needed to know by saying "My two travelers should be my gold screws". Mystery solved for me and the simple data point I needed to understand 3-way switches. I ran in the house and easily solved my issue by ensuring the gold screws were connected to the two wires in the same sheathing. Thanks!

[TeslaRebuilders]

My favorite 3 way problem was mixing it with a fan and light leg from another 3 wire. It's so easy to confuse especially when cutting in the switch box if not labeled well. I started putting each switch leg and traveler in its own position in the box to help prevent mixups.

Maybe you could demonstrate a more advanced problem say in a 4 gang box with multiple 3 ways switch legs and a fan leg combination.

[fuzzyfuzzwuz]

as soon as you demonstrated the problematic behavior at the start of the video, I knew that this was exactly the video I was looking for!! I goofed a 2-way switch that sits in a 3 gang box when I was trying to install a dimmer switch and with so many wires in the box I've been trying to understand which wires I goofed up. FINALLY after months, this video helped me restore normal functionality to our 2-way kitchen lights. THANK YOU!!

[Stinky_sack]

Please do more videos on troubleshooting. I'm a new journeyman and feel behind on what I should know when it comes to troubleshooting

[musicalheart]

You are a God send! I didn't even realize I had switched my hot wire and traveler wire around. I had two black wires and one white one and no clue how to figure out what went where.
Your very detailed explanation helped me tremendously 😊Now everything works. Thank you so much.

[evantyler]

I was going CRAZY! And didn’t understand anything you said until you explained both travelers are coming out of the same spot…. NOW MY 3way works! Thank you so much

[_JesseRosa]

Swapping out old 3-ways in a 1964 house I just bought. Was so confused why they weren't working properly after the swap

Watched this video & when you said to look at the sheathing to see which one had 1 wire coming out & which one had 2. Thats all I did & now it's fixed good as new!

You're the man thanks so much

[mikeTHEmanatee]

Dude, the upgraded version of that Milwaukee drill is my most used drill in residential. It's around the same size maybe even more compact (yet looks beefier) but an awesome feature the newer model has is it has 2 speeds, and both a drill mode and screwdriver (clutch) mode. I throw a 6.0 12V battery on that sucker and it'll last all week, but most importantly it has the capability of drilling light holes, in wood, stucco. Really saves the day if ever you're in a pinch or you don't want to have to climb down the attic or back down the ladder and to the truck for a drill driver gun. I Def recommend. Thanks for the videos

[moelassus]

Just today I was in the middle of swapping all of the switches in my house when I lost track of the wire positions on a 3-way. Initially I panicked but this video helped me resolve it in quick order. Thanks Dustin!

[michaelwells]

~ I can see why your content qualifies for continuing Education .... I learn alot from it ~ that I didn’t quite get from my AA Building inspector degree instruction

[jluke]

Thanks Man! I had this exact problem and thanks to this video I learned how to fix it. The important part that allowed me to see what went wrong was where you identified that the 2 travelers needed to be in the same sheath. Great instruction!

[blueskies]

Love this! My first job as an independent, was to troubleshoot and fix ALL of the 3-way switches that had been mis-wired in a 6, 500 sqft house in University Park. It was a great learning experience for me and established my regimen for wiring 3-ways. During rough in, I'd give the two travelers a couple of twists together to identify them and leave the common (hot or switch leg) alone. Now I've seen some electricians then coil the common around the travelers and I can see how this would be helpful in multi gang boxes with several travelers (and even multiple commons, a mix of hot(s) and switch legs). For temporary lighting, I might cap the common with a traveler (usually the black) and just install one temporary switch (single pole or 3-way) at the other side. At final trim, I would attach the lonely black to the common, the red traveler to the gold screw on the side of the common and the remaining black to the solo side gold screw. Rinse and repeat on the other end and I've never had a problem.

When troubleshooting customer installations, this is the first thing I, reconfigure the wires as I've described. I've never seen a 3-way switch 'fail' however I have found several single poles that have physically stopped working. They normally feel 'squishy' or 'loose' when operated. Only once have I had a 4-way fail on me.

The worst experience was my first 4-way installation when the boxed 4-way switch had been replaced with a single pole by some devious customer that wanted to save 10 bucks and rip off the big box store. I lost three hours finding out I had the wrong switch then having to make another run to the store. Now I physically inspect boxed switches before I buy them.

[Bigjoedo]

Thank you for the Video!! Someone put a red traveler on the hot lug. The other end was wired to a dimming switch. When I took the switches out the hot wire was 12 gauge and the travelers were 14 gauge. I replaced both switchs as you instructed on another video and it works great!!

[davidanderson]

“Your travelers are always going to be in the same sheathing.” Thank you!! Problem solved.

[CajunGreenMan]

I was just learning about this in SkillMill, so this was a great additional review. Keep up the great work!

[RichardMelaas-hxhz]

Great explanation on how to figure out which wires are the travelers and which wire is the hot wire without needing a multi-meter.

[youdontknowme]

There used to be these push-button 3-way switches decades ago, so the position doesn't matter, just press. I miss those.

[jeffreymoen]

I had the exact issue. Watched your video and fixed the issue in a couple of minutes. Thank you!