How do you Install a Light Switch

how to install a light switch

Seconds after this photo, I realized I had a big problem. Be sure to read Step 4 to see why this light switch installation was only just beginning.

How do you install a light switch? It seems simple enough. Just walk right up there and install it.  No problemo.

I remind Charlotte and Christian about 2000 times per year to turn off the lights in the basement after feeding the cats.  Sometimes they remember, other times, not so much.

Regardless, each night I have to trudge down to the basement storage room, which is about 8 leagues under the sea, and check.

The solution.  Install a new motion sensing light switch.  On the surface installing a light switch seems easy.  Heck, even the back of the box shows it in 3 easy steps.

Except, it's not so easy if you haven't done it before. At the end of the post I have a list of 4 gotchas that make this easy project... hard. But first, let's start with the basic light switch installation steps.

How do you install a light switch

Before you can install a light switch you need to have a light switch.  In this case I'm installing the motion sensing switch with a timer and a on/off button that you see above.  The process is more or less the same for a dimmer or three-way switch with some minor twists and turns. More on those in a later post.

  • how do you install a light switch - breaker box

    When installing a new light switch first kill the power to that switch.

  • Step 1:

    Find and kill the power to the light switch that you want to replace.

    See, it's easy, here's my power panel.  Just read the chicken scratch and then flip the breaker to off.

    If you haven't labeled your breaker box yet, well, now is a good time. Just start flipping off breakers and when your wife/husband starts yelling at you... then you know you've found the breaker for the TV plug.

    In this case I'm replacing a light switch in the storage room of the basement.  The electrical panel is in the same room.  I know I've found the right one because the lights go out.

  • replacing an old light switch - old dirty one

    I swear... we do clean our house. This old light switch needs to be replaced with a motion sensing switch.

  • Step 2:

    Remove the cover from the old light switch and test the line for power using a voltage tester.

    Yes, I know you killed the power. You should still test with a voltage tester. The alternative is electro-therapy.

    Feel free to give me grief for the dirty cover in the comments but this is one reason I'm replacing the switch with a motion sensor. No more grubby hands touching the light.

  • replacing a light switch - step 3

    Keep track of the wires so you know where they go when installing a new light switch.

  • Step 3:

    Loosen the terminals (the screw thingies) on the old switch and remove the wiring. 

    Okay. So you've tested for power and you're good. You've unscrewed the old switch cover and pulled out just the switch. Now you need to unscrew the wires from the terminals.

    If you're not sure at this point whether or not the power is out... you are about to find out, in person.

    If you're replacing a switch you may see some other wires tucked in behind the existing switch. Leave those little piggies at home. They are probably carrying power to other parts of your house. Just worry about what's hooked up to the light switch. (if your switch has an extra "white" wire, tie that into the other "white" wires.)

  • install a light switch installation - hooked up

    Operation... "You're the Doctor". Remember that game??? Wishbone? Seriously?

  • Step 4:

    Hook up the new switch to the existing power and neutral wires.

    If you're Mac Daddy like me and bought a fancy new timer switch or something cool like that then you'll probably notice that it doesn't have terminals.

    Instead it has three wires coming out that you will need to join together with the existing power wires using some wire nuts.

    You may also find that your enthusiasm for this "small" project is rapidly waning  as you realize that your new switch is not going to fit into the old box!!!  Mother TRUCKER!

    "You're gonna need a biggerboat electrical box " -  Brody from Jaws  (sorry youngsters, Jaws is an old movie about a Shark that ate everyone)

  • how to install a light switch final

    That's how you install a light switch. Works great and the kids love it!

  • Step 5:

    Turn the power back on. Test. Turn power off. Seal everything back up.

    So what happened here was the original electrical box was way to small for the new and much larger switch. Not to mention the fact that there were now three more wire nuts than before because the new switch didn't use terminal screws.

    I went to Home Depot and talked to Wayne. He recommended this new box that they're stocking which has an awesome little extra space that I call a "side-car"

    The new box had plenty of space. The only draw back was that I had un-wire everything in order to install it.

4 Gotchas that make installing a light switch difficult

1. Your breaker panel isn't labeled - You end up spending an hour just figuring out how to start. Label all of them today! One time and you're done.

2. You don't have real wire strippers. So you try to use a utility knife and some pliers but you end up damaging the wire or worse, cutting yourself bleeding all over your new switch. [Been there... done that.  Buy wire strippers]

3. The box is to small.  I ran into this problem just doing this project. Granted, this one takes a bit more work to fix but it is still fairly easy. Just take a note of the box size before you start. If it looks to small it probably is. Prepare ahead of time to put in a new one.

4. You wire something incorrectly - For example, in the project above I thought I twisted three black wires together but in fact one was not tied in correctly. The lights in the work room were not coming on even though my new switch worked fine. I had to go back and carefully recheck my work.

basement finishing jason

If I had had everything I needed I probably could have changed that out in about an hour.

To avoid frustration prep all of the materials you'll need a day before you attempt the project. Here's a picture of all the tools I ended up using.

It's a great project to start learning how to do electrical projects around your house. When you're ready for the next level it's time to get your learnin' on. Check out these electrical "how-to" books that I used to teach myself how to install a light switch and much, much more.

Cheers - Jason


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Questions and Comments

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  1. says

    I love this blog post! It made me laugh.

    I don't have a basement but I do have an attic, does that count? Of course you have to walk around it like Quasimodo (don't worry, kids, that's a reference to an old book), but it could definitely use a motion-sensing light switch.

    • says

      Of course it counts. Basement, attic, mud room where you cut your teeth doesn't matter, the destination is the same. Complete mastery of your house and how it works. The motion sensing switch has been great!

    • says

      Thanks Hannah. Hard to believe but summer is coming up and we're headed to the beach about a month from now. The house has a great little theater room just off the pool... perfect for watching JAWS!

  2. David says

    LMAO - I couldn't keep reading after "If you’re not sure at this point whether or not the power is out… you are about to find out, in person." I was laughing too hard. AWESOME!

  3. Phillip Morrison says


    First of all, thanks for inspiring me to finish my basement on my own in under a year. I started January 1st and finished all the framing on March 1st. You have great time saving tips and it has helped. I am going to buy all my electrical equipment this weekend to start electrical on the basement. I have some lights and plugs there now, but plan on running all new wire and removing all of the old once the inspection passes(before drywall of course). I bought and read the 2 books you suggested and watched the videos you posted, but I can't seem to get an answer to an easy question. Thought you could help. Is it ok to have plugs and light switches on the same run? I don't want the light switch to control the plugs, but also don't want 15 different runs on electrical in my basement. I'd like to have one run for each room if possible. Is this possible and what is the best way to do it? Plugs then lights or lights then plugs?

    • says

      Hello Phillip - So glad the website has been helpful with finishing your basement. Yes, you can run plugs and switches on the same run. However, you cannot mix wire guages. Typically plugs are 12 gauge and lighting is 14. If you plan to mix plugs and lights then you should run 14 for both. This may limit what you can put on that circuit. For example, you couldn't plug in and run a treadmill.

      Instead of a circuit per room, I recommend 2 or more plug circuits, going to all rooms. Then two or more light circuits. It sounds logical to have a circuit per room but that's not how it's typically done. Hopefully this helps answer your question. Good luck on your electrical! - Jason

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