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How to replace your old, outdated 3-way light switches / Brian Bennett

Archaic light switches might as well be from the stone age. All they do is turn a light on and off. They can't dim lighting gently or remember the brightness level you prefer. Outdated switches don't play nicely with LED bulbs either. The solution? Swap them for modern switches.

This guide will take you through the steps of replacing those aging three-way light switches with updated wall controls. This process can be tricky, so read through the steps before you start your project. In some cases, it might be best -- and safest -- to contact an electrician.

Tyler Lizenby/CNET

Step 1: Locate your switches 

The most basic three-way switch setup has two switches that connect and control one light fixture, like switches on either end of a hallway, staircase or large living area. In most cases the light (or array of lights) they operate sit on the ceiling above. Specifically these are hard wired lights, not merely lamps plugged into outlets.

Tyler Lizenby/CNET

Step 2: Gather your tools

You won't need many tools for this job. The necessary supplies though are critical so make sure you have them on hand. Here's the list:

What you need

  • Philips and flathead screwdrivers
  • Pen voltage tester

Have these just in case

  • Electrical tape
  • Wire nuts
  • Wire stripper or lineman pliers

Optional but kudos if you own one

  • Multimeter (aka multitester)
Tyler Lizenby/CNET

Step 3: Turn off the power

Safety should be a priority with this project and that starts with killing power to your outlets. Before you do anything, switch off the breaker on your main electrical panel. Target just the breakers that handle power for the light fixtures and switches you plan to service.

Tyler Lizenby/CNET

Step 4: Access the wiring

Now it's time to get at your wiring. There is often a pair of screws holding each faceplate in place, at the top and bottom. Unscrew these screws then remove the plates covering each switch.

A common practice is to wrap switch terminals with electrical tape once their wires are connected. In my case, the old switches had exposed terminals so I made a mental note to tape them later. Just to be safe, use a voltage pen to check for a live current. With your voltage pen turned on, tap the edges of the switch. If the pen starts to flash and sound its alarm then watch out! There's likely high voltage (120 volts) electricity running nearby.

Of course if you need to measure the actual voltage of live wires, a multimeter is the way to go. This gadget can sniff out voltage and amperage of electrical circuits, components and connections. Learning to use this tool is a valuable skill.

Once your pen gives the all clear you can proceed. If not you'll have to switch more breakers off at the main panel until the warnings stop.

Tyler Lizenby/CNET

Next, remove the screws that hold the old switches in place. They're in tabs on the top and bottom of each switch. The screws also bore into holes on the electrical box behind them. To access the wiring, gently pull the switches out of the electrical boxes. Be careful not to dislodge any wires from the switch terminals -- the wires should still be firmly attached to the screws on the switch holding them in place.

Before you dive in, take a second to snap a picture of the switches and visible wiring. In fact, take photos before and after you tinker with anything. This way, you'll have a record of how everything was connected (and working properly) initially. Think of it as extra insurance in case you run into trouble along the way.

Tyler Lizenby/CNET

Step 5: Assess the wiring situation

You should now have a good view inside each box. I must stress that there are many possible ways a set of three-way light switches can be connected. This step-by-step is reflective of a common wiring scenario and the one in my own home.

Inside each of the two electrical boxes you should see two bundles of wires. Let's call each box "Box 1" and "Box 2." We'll also assume that, like mine, the boxes you're working inside are on a floor above the basement. If so then the direction wires enter each box is important. It will help you deduce their origin and ultimately identify them.

Box 1. In box 1, one of the wire bundles enters the box from the bottom. This three-wire bundle should consist of two colored wires (black, white) plus one of bare copper. These wires come from your home's main electrical panel (usually in the basement below) and provide power to your lighting circuit.

The other 4-wire bundle will enter the box from the top and have three colored wires (black, white, red) and a copper (bare) one. They connect the switch in this box to the other switch in box 2.

Box 2. Here, both wire bundles should enter the electrical box from its top side. Besides their direction of entry the wires are constructed the same way. One three-wire bundle will have two colored wires (black, white) plus one of bare copper. These link the switch to your light fixture. A second bundle (four-wire) should contain three colored wires (black, white, red) and a copper (bare). The wires here connect this local switch to the other in box 1 across the room.

Step 6: Decide to proceed or abort

The wiring you see may not match what I've described. For instance, there may not be any white wires. This scenario tends to happen with switches in older homes. One of your electrical boxes might have just one bundle of wires while the other is packed with three bundles. 

It isn't uncommon either to have one three-way switch in the same box as two or even three others. All those switches, terminals and wires can confuse experienced electricians, let alone novice DIYers.

Take a look at these two diagrams below. The first is an outline of what you should see. It's the simple three-way circuit I anticipated and encountered in my home. The second drawing depicts when box 1 has three bundles of wire while box 2 has just one.

Steve Conaway/CNET

If your lighting setup doesn't jive with these two pictures, I suggest you abort the project. The same goes if the wiring is mysterious, odd or looks complex. You'll be better off playing it safe and hiring a professional.

Steve Conaway/CNET

Step 7: Swap in your new switches

If your wiring matches my description (diagram 1) or what's shown in diagram 2 above then proceed. Be advised that for diagram 2 layouts you will have to adjust my instructions accordingly. If you haven't already taken a photo of the original wiring, now's the time.

In Box 1, disconnect a wire on the old switch and attach it to the correct terminal on the new one. Methodically dealing with one wire at a time will help avoid confusion and mistakes. The black wire from the three-wire bundle (coming up from the main panel) links to the "common" terminal (also called line) on the new switch. This terminal should be painted black on the switch or labeled "COM".

Tyler Lizenby/CNET

The black and red wires in the other bundle (four-wire), entering the box from up top, are the travelers (wires from the other switch). Attach these two wires to the two brass switch terminals. For these it doesn't matter what silver terminal you use.

Similarly, inside Box 2, attach the black wire from the three-wire bundle (black, white, copper) to the black terminal on the new switch. Attach the red and black wires from the other bundle (four-wire) to the switch's brass terminals. Again these are the travelers that connect both three-way switches in the circuit.

Tyler Lizenby/CNET

In my particular case, the Lutron switches I bought had one brass and one blue terminal. Since they're made to work as a pair, I made sure to attach the red traveler wire to the blue terminal on both switches.

Tyler Lizenby/CNET

The last link to make is the ground (bare copper). Each electrical box should have a bundle of copper wires joined together with a wire nut (the yellow twist-on wire connector, pictured below). In some older homes, these bundles predate wire nuts and are simply soldered to each other. Regardless, the bare copper ground wire attaches to the green terminal on your switches.

My new switches, like many others, have a green ground wire that was pre-attached at the factory. With a few twists of a wire nut, I added this green wire to the group of existing copper wires which for the record were soldered together.

Tyler Lizenby/CNET

Don't worry about fiddling with the white (neutral) wires. While they're necessary for the lighting circuit to function, ordinary switches don't require this connection. Smart light switches, though, tend to need a neutral wire hookup. These white wires should be connected already. If not, link them together with a wire nut.

Tyler Lizenby/CNET

Similarly, inside box 2, attach the black wire from the three-wire bundle (black, white, copper) to the black terminal on the new switch. Attach the red and black wires from the other bundle (four-wire) to the switch's brass terminals. Again these are the travelers that connect both three-way switches in the circuit.

Don't forget to attach the copper ground wires to the switch the same way you did in box 1. Likewise you should confirm the white (neutral) wires are squared away here as well.

Tyler Lizenby/CNET
Tyler Lizenby/CNET

Step 8: Test the lights

Now comes the moment of truth. Flip the power back on at the main panel and test your switches. If your new switches sport slick LED indicators, you'll know right away that they're working. Give yourself a pat on the back, you've earned it. And if you ever want to install sophisticated smart switches down the road, congratulations. You've gained the skills to tackle that as well.

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