wiring-a-three-way-switch-pic1Wiring a three way switch will be necessary when you deal with this type of switch in your home. Simply put, a three way switch consists of one light that is controlled by two separate switches. When you toggle either switch up or down, you turn the light on and off. A great feature for rooms that have more than one entrance to them. They are very common in modern homes. The problem is from a wiring stand point they have some unique requirements.

Not sure if this is your problem? See the articles 'Troubleshooting Electrical Wiring' and 'Residential Electrical Repair' for a listing of related articles.

The simplest schematic possible has the power for the light coming in one of the switch boxes. Two hot wires going between the two switch boxes. From the second box a hot wire would go up to the light. Your house may or may not have been wired using that configuration.

Any other combination will result in a white wire (usually the neutral to be used as a hot traveler). We are not discussing installing rough in wiring in this article. Instead we are dealing with the switches themselves and the correct hook up for them. Still for the sake of understanding we are including a couple of paragraphs on the correct wiring. See Step One for wiring a three way switch rough in requirements.

Wiring a Three Way Switch - Information

What Can You Save?

Prices will vary but it will probably cost between $40 and $150 to have someone come out and replace a light switch for you. A three way switch costs around five dollars (more for dimmers) and take ten to fifteen minutes to change. Your savings could be between $35 and $145, not bad for fifteen minutes of work wiring a three way switch. Installing a three way where you did not have one previously is another matter entirely. You could be looking at hundreds of dollars.

How Hard Could It Be?

Wiring a three way switch is not that difficult.

These repairs will have a Difficulty Level of: A Bit of Work
These repairs require a Skill Level of: Determined Handyman

Check the Simple Things!

Check the bulbs first. Yes it is possible to get a brand new bulb out of the package and it be bad. Try a second one of the first one still does not work. Loose wires on the switch would be the next simple thing.

What Can Go Wrong?

Electrical shocks can cause severe injury and even death. Be careful, make sure the power is off. Always double check, turn the breaker off and then use a tester to make sure nothing is hot. It is possible for more than one circuit to be fed through a single box. Faulty or incorrect wiring can cause dead shorts and fires. Make sure you understand how to hook something up before you attempt it. A three way switch that is wired incorrectly may do weird things. The light may work with certain combinations of the switches, but not with others.

Understanding Three Way Switches

For a typical homeowner, understanding the intricacies of a 3 way switch can be a little challenging. Unless you are an electrician, in which case you are probably not reading this article. The whole purpose of a three way or four way switch, is the ability to control a single light or bank of lights from more than one location. Where things get interesting is when you have to coordinate electrical power between the switches and the lights.

For the rest of us, a three way switch has 'three' terminals. The 'single' terminal on one side of the switch is either the power or it provides the power to the light, no other choices. The other side of the switch has two terminals, these are often called the travelers. All this means is that they travel between the two switches. Both of these 'travelers' have power in them and when the switches are flipped, the light turns on, amazing?.

When you are replacing a 3 way switch the best thing to do is change the wires over to the new switch in the same position as the old switch. You will be sorry if you go online and start looking at wiring schematics for three way and four way switches. They can be confusing for more than one reason. The primary reason is that there are multiple ways that a 3 way switch can be wired. You may or may not find the schematic that matches what you have. To make matters worse, without spending a lot of time testing wires, you don't know how your three way switch is wired.

How a Three Way Switch Works

wiring-a-three-way-switch-pic2How a three way switch works? Now that is a great question. Simply put, two switches control a single light. So, each switch always have to have power available to it. That is the tricky wiring feature.

The answer to how a three way switch works, is to have an extra hot wire that runs between the two switch boxes. Most residential wiring is done with 12-2 w/ground or 14-2 w/ground sheathed cable. This type of cable consists of a Black, White and Bare Copper wire.

The cable that runs between the two switches needs to be either 12-3 w/ground or 14-3 w/ground. This gives you a Black, Red, White and Bare Copper wire. The extra red wire allows for the ability of power always being available to the light, no matter which way the switches are.

From a wiring standpoint, you want to bring the heat (power) into one of the switch boxes. Between the two switch boxes you run the wire with the extra hot wire. From the second switch box, you run a standard cable to provide power to the light.

Sounds simple right? It is as long as you follow the schematic that is provided with the switch. There are several possible wiring variations, for some information on some of the possibilities see this site, 3 Way Switch Variations. It provides diagrams for the various options.

WARNING!! Make Sure the Power is OFF!!! BEFORE You Work on Electrical Devices!!!

Replacing a Three Way Switch

wiring-a-three-way-switch-pic4Replacing 3 way light switch, or if you want to use proper grammar 'replacing a three way switch' begins with obtaining a new switch. With an existing three way switch in place the change over is not too difficult. You will want to leave the existing switch in place until you have the new one ready to install. Remember, do not work on any electrical device until you have turned oof the power.

Purchasing a 3 Way Switch

Finding three way switches to purchase is not hard at all. Home supply, big box home stores, hardware stores and electrical supply stores will all have them. What may be challenging is finding the particular color and style that you want. Use your phone and take a picture of the existing switch or the new style you are trying to match before you go to the store.

A new three way switch should cost less than ten dollars unless you have something special in a decorator style. The wiring functionality of the switch should be the same, no matter what switch you choose.

Understanding Three Way Switches

Understanding three way switches can be difficult for a novice. Even those experienced with electrical wiring struggle with them at times. The confusion starts with the term 'three way' or '3 way'. Actually, it is two switches controlling one light. So where does the 'three' come from? Well, it is the number of poles on the switch itself.

Replacing 3 Way Light Switch

Before you begin replacing a 3 way light switch, the first thing you will want to do is turn off the power to the switch. Put a piece of tape over the breaker so that no one inadvertently turns it back on.

This happens when the your wife is ironing and she thinks the breaker tripped. In fact let everyone in the house know that you will be working on the electric. Check with the tester to make sure that it is dead. Remove the cover plate and then unscrew the switch from the box. Three way light switches have three lugs that need connections.

Pay particular attention to which wire is hooked to the black lug, or the single terminal on the switch. Make sure the you hook the same wire to the black lug on the new switch. If the lug is not black it should be the one by itself on one end of the switch. The other end will have the two alternating hot legs on them. It does not matter how you attach the wires to the two terminals.

Three Way Light Switch Replacement Suggestions

wiring-a-three-way-switch-pic5Tagging 3 Way Switch Wires

You may have any combination of Black, Red and possibly White wires attached to the switch. It might be a good idea to tag the wires with tape before you take them off. Mark the wire on the black lug 'B' and the other two 'T1' and 'T2'. The 'T' is for traveler.

At any given time this is the situation you will have with the two three way switches. One of the wires hooked to the black lug will be hot all the time. The wire attached to the black lug on the other switch will be hot when the light is on. One of the two traveler wires will always be hot. They will alternate when the switches are flipped. A ground wire may also be connected to a green grounding lug.

Take the new switch and line it up with the old one, with the black lug turned the same way. It might be a good idea to put some pieces of tape on the locations for the existing wires. Use the Same 'B', 'T1' and 'T2' designations.

It might be a little redundant, but if you get called away and have to come back. You might not remember which wire was which. With every thing marked, check one more time that the power is off. Unhook the wires from the old switch and attach them to the new switch.

Positioning Three Way Switch Wires

Another approach that is employed by professionals is to turn the wires in a certain direction when you remove the switch. Remember, the one you want to keep your eye on is the single wire that attaches to the single lug on the switch.

When you disconnect that wire, (power off, remember), turn it up or down, depending you how it was hooked to the original switch. The other two wires can be turned in the opposite direction when they are disconnected. You can keep them to the right or left, depending on how they were attached to the original switch.

When you use this method, even if you are called away, the connections should be self explanatory when you come back. This method is simple and straight forward.

Installing a New Three Way Switch

Attaching 3 Way Switch Wires

At this point you have marked or positioned your wires so that you know where they go on the new switch. Attach the single wire first, POWER OFF, CHECK IF YOU ARE NOT SURE, it goes on the single lug on the switch.

Then attach the to 'travelers' to the other two lugs. If you took the time to mark or position the wires, you can attach them to the same lugs on the new switch. The position of thes two wires is not critical, transposing them will have no impact on the operation of the switch.

The new switch may have a grounding lug on it. If there is a ground wire available in the box you can hook it up to the green lug. Grounding of light switches is a new development in wiring and code practices. It is another safety precaution that can prevent shocks.

Wrap electrical tap around the bare lugs on the switch. This is just an additional safety precaution for you or someone else that may need to work on the switch in the future.

Testing Your Three Way Switch

Turn the power back on to make sure it is working properly. Does the light work? Check both switches to make sure that everything is functioning correctly. Screw the switch back into the box and install the cover plate. That's all there is, congratulations!


Are you done with your wiring a three way light switch project. We hope it was successful. A few tools and a few minutes should have taken care of it. Maybe a little longer, since you had to mark those confusing wires on the switch. Even longer if you didn't mark the wires and to work with trial and error.

What are you going to do with all the free time you have? Take a look at your list and decide on another project you want to tackle. Now that your confidence has been built up by this success story.