I have a porch light controlled by a wall switch in my entryway. Rather than having to manually turn this light on at night and off in the morning (or worse, forgetting and wasting energy having it on all day), I wanted to install a timer where the existing light switch was to automatically do it for me.

Now, there are several different types of programmable timers.  Some are mechanical.  Some are digital.  Some require only two wires, while some require more.  Some require a battery; others don’t.  I’ll walk you through all of these options so you get the right one.  Before you buy the timer, you will need to do a little investigation to determine which type of wiring you have, which will determine what type of timer you can use.

Note, if you are not comfortable using a voltmeter to measure the voltage of household wiring, then you should probably leave this project to a professional electrician.

Note: This is a professional review site that receives compensation from the retailer or manufacturer when you purchase through the affiliate links such as the ones below. I test and/or research each product or service thoroughly before endorsing it. This site is independently owned and the opinions expressed here are my own.

Is the existing switch a three-way switch?

The first thing to determine is whether the existing switch that you want to replace is a three-way switch or not. A three-way switch is when two switches control the same light. This is often the case in a long hallway or staircase, where you can control the hallway light from either end.

The options I discuss in this article only cover the case where one switch controls the light, or a “single pole” switch. Three-way switch wiring is more complicated and will require a timer that is specifically for three-way switches. Luckily, most things that you would want to put a timer on, like a porch light, only have one switch controlling them. But, double check to be sure, and note which type you have so you buy the right kind of timer.

Do you have a neutral wire in the switch box?

This is actually the trickiest part of the project, but doing this before you go out and buy a timer can save you the hassle of going back and returning it. Before buying anything, you need to find out if your switch box has the neutral wire available. New homes are required to have a neutral wire, but if your home is old, it might not have it.

To find out, first shut off power to the switch you’re working on by turning off the respective switch on your circuit breaker. Some experimentation might be necessary to find the right circuit breaker switch controls the light. Turn on the light and go through your switches to find the one that controls that light.

Next, unscrew the cosmetic wall plate and put it aside. Once the switch box is exposed, unscrew the switch and pull it out slightly so that you can see the wires that are available inside the box.

You then need to figure out how many different types of wires are available inside that box. The answer will be at least two, since the switch needs a wire coming from power and a wire going to the light in order to work. One of these wires is power (“hot”), and the other goes to the light, or the “load”, as it is called.

The neutral wire is usually white. Note that neutral is different than ground.  The ground wire is often bare copper or sometimes green.

The summary of the four possible types of wires you might have are as follows:

  • AC power or “hot” wire: goes to the existing switch, sometimes red, blue, or black, often bundled together with other wires of the same type, sometimes comes from a cable or conduit with Neutral and Ground wires in it. If you measure the voltage using a volt meter (after carfully turning the power back on at the switchbox), you will find about 115V AC.
  • Power to the light bulb or “load”: goes from the other pole of the existing switch to your light, sometimes black also, usually a single wire not tied to any other wires. If you measure the voltage using a volt meter, you will find 115V AC when the switch is on, and 0V when the switch is off.
  • Neutral: usually white, often tied to other white wires, sometimes comes from a cable containing AC and Ground.
  • Ground: usually bare copper or green, often tied to other wires of the same type, sometimes comes from a cable containing AC and Neutral.

So, the question is, does your switch box only have two types of wires (“hot” and “load”), or does it have a neutral wire as well?

When I opened my switch box, the wires looked like a plate of spaghetti. To make matters worse, many of the wires were covered in white paint so they all looked white. But, after some careful observation and some volt meter measurements, I was able to ascertain that I had all four wires. That was good, because I had already purchased a timer that required four wires!

This was my "plate of spaghetti" that was in my switch box. After careful investigation, I was able to figure out what each of the wires was for.
This was my “plate of spaghetti” that was in my switch box. After careful investigation, I was able to figure out what each of the wires was for.

Don’t chance it like I did! Look at your wiring BEFORE you buy your timer! The packaging or description should say what wires it requires. In my case, the product packaging said “Neutral Wire needed for installation”.  Also, if the timer is not battery-powered, it will need the neutral wire. If it is battery powered, it won’t.

Note that if your switch is a three-way switch, the switch box will have an extra wire in addition to the ones I’ve described above!

Types of timers

Okay, now that that painful step is out of the way, I can start talking about the pros and cons of the different types of timers.

Two-wire timers

Two-wire timers don’t use wall power to run. Many two-wire timers require a battery, so watch out for that!!! There is at least one that is purely mechanical and doesn’t require a battery (the Intermatic EJ351; note that the instructions for this say it only works with incandescent bulbs, not florescent). These are super simple to install: just remove the existing switch and connect the timer to the two wires that used to be connected to the switch.  Of course, you can use a two-wire timer even if you have four wires available.  If you are intimidated by electrical wiring, this is the way to go.

Three or Four-wire timers (neutral wire present)

Why, then would anyone go with a timer that requires a neutral wire? First, these tend to be less expensive, and they don’t require a battery that will need to be changed. The neutral wire allows them to run off of wall power. These types of timers tend to be simpler in construction and are less likely to fail than two-wire timers. If you have a neutral wire available, and you’re comfortable with household wiring, then these timers are preferable due to reliability and no need for battery.

Note that you can have an electrician add the extra neutral wire to a two-wire setup, but that is more hassle than just getting a two-wire timer, and probably not worth it.

Mechanical vs. Digital – My Recommendation

Digital timer. This type of timer is almost impossible to program without the instruction sheet, and the tiny display and buttons are difficult to work with.
Digital timer. This type of timer is very difficult to program without the instruction sheet, and the tiny display and buttons are a pain to work with. The relay in this one failed after a few years.

The next choice you’ll have to make is whether to get a “mechanical” timer or a digital timer. In a mechanical timer, a motor turns the dial which mechanically actuates a switch that turns on or off the light at certain times. In a digital timer, a microcontroller activates a relay which turns on or off the light. In my personal experience and from what I’ve read online, digital timers are less reliable. (Just look at online reviews if you don’t believe me.. Some reviewers online buy two at a time because the relays fail so often!)

But, there is another advantage of mechanical timers: they are way easier to program! My first timer was digital, and was a royal pain to program. Unless you enjoy pressing tiny buttons repeatedly to increment numbers on a tiny screen while reading tiny text on a tiny instruction sheet, stay away from digital timers!! I found my digital timer very difficult to program, and I have a degree in electrical engineering!

A mechanical timer, on the other hand, usually consists of a dial with some switches that indicate when the lights are to be on and off

.  With one glance, you can see the on and off periods, and it’s intuitive how to change those times, as well as how to set the time after a blackout (simply turn the dial!)  They are not as sleek-looking as digital timers, but believe me, you want this simplicity!!!  You’ll be able to program a mechanical timer without needing the instruction sheet (which you will probably lose)!!

Okay, I hope by now I’ve convinced you to get a mechanical timer with a wheel, not a digital one with buttons and a display. Here is the one I used and recommend (Jasco Products Company 15325 Indoor In Wall Timer):

Jasco Indoor Wall Timer
Jasco Indoor Wall Timer

Please be aware that it requires four wires (i.e., neutral).

If you have only two wires available, you’ll need to get a two-wire timer that requires a battery.  If you have the neutral wire, and are comfortable with doing the extra wiring, then get a four-wire timer.


OK, if you did your homework and identified the types of wires available, then installation will be a breeze.

Make sure power is shut off at your circuit breaker and follow the instructions that came with your timer.

If you need to connect to a large bunch of wires, then use the electrician’s trick of using electrical tape to hold the wires together (tape around the insulated area, not over the exposed copper) while you screw on the twist-connector.

After all of the wires are connected, turn on power at the circuit breaker and test the timer. If all is well, screw the timer into the wall, and re-attach the cover plate.

My installed mechanical 4-wire timer
I installed the mechanical 4-wire timer on the left. You can tell at a glance when the light will be on by the tiny switches going around the dial (pushed towards the center for off, and out for on). This particular model is the GE Basic Timer, Indoor, model 15325 from Home Depot or Amazon.

Hope this has been helpful! Please comment on your experience below! – Brian


  1. I want to replace an existing bathroom vent fan switch with a timer. The trick is that the fan switch is half of a single-switch-sized unit, and I have not yet been able to find a replacement product that in the same way combines a separate light switch with a fan *timer*. Does anyone know whether such a product exists, and if so, where I can find it? I can’t believe I’m the only person in history ever to need this.

    (Due to space limitations, I do not have the option of simply replacing the single box in the wall with a dual box, and mounting an ordinary light switch al9ngside a full-sized fan timer. I could mount a second single box/switch *above* the existing one, but that would be ugly. Plus it would involve cutting into drywall, something I have not done before and which therefore makes me leery.)

  2. Brian,
    I have a three year old house and I want to put a timer on outdoor lights–to turn on/off while away for extended periods of time. One porch light and two outdoor wall lights — all controlled by same switch–not three way.
    The current on/off switch is in a three gang box. Multiple wires abound…but ultimately two white wires going to the switch plus a ground. Dont have a volt meter so cannot tell exactly what I have going on??
    In your picture of spaghetti above-it looks like you have only two wires to the switch. But in the article just before the picture, you said you have four wires. I’m a bit confused.
    Stupid question, but could there be a neutral in the wiring AHEAD of the switch itself–that is not connected to the switch? Any help/clarification would be appreciated.
    Thx in advance…

    • Hi Patrick,

      First of all, I would not recommend doing any electrical work without a volt meter.

      My photo shows two wires going to the existing two-wire switch. But, the wall had four wires; not all were used with that old timer. They are used with the new timer I put in.

      It sounds like you have three separate wires going to your switch, so therefore you could use a three-wire timer, but I am not certain. Sorry I can’t be of more help.


  3. My wall box has 3 wires, black, white and copper(ground)….I have the same switch you show in the pic….it has 4 wires, red, black, white and green. I have tried connecting red and black to black, white to white and green to copper, no go. I tried just black to black, white to white and green to copper, no go. I tried red to black, white to white and green to copper and still no go…..sounds like a bad switch or ?????

  4. Timers shouldn’t impact whether you use CFL or LED bulbs. So, you should be able to continue to use the existing timer.

  5. Seems pretty straight forward, however once I got my four-wire digital timer to work on the porch light, the other two light switches, which operate lights in the front room, ceased working. The other two switches did not use neutral. Both were connected to the same ground wire via splice. Each has hot and load. I did not change a thing on the existing light switches.
    New house…4 white wires were bundled and available. Does it matter which two I use on the timer?
    I’m about to put the original switch back in…but would appreciate your thoughts first.



    • Hi Phil,

      Did you keep the 4 white wires bundled together? These might go to the other light switches and might need to be connected.


      • Thanks for the reply Brian. The white bundle was not connected to the other two switches. I simply took one from the bundle and the one for the porch light and plugged them into the timer switch.
        I get that the other end of the white cables in the bundle go to the light. What’s my best option here, a splice?



        • Clarification – the bundle is FOUR white cables. Do I splice off of two of them to plus into the timer switch? Is asks for two neutral connections.

        • Hi Phil,

          Sorry, it’s difficult for me to know what to do without doing some measurements to see what those four cables are for. My gut is that they need to be connected together.


        • Gotcha. The timer calls for a hot wire, a load wire, two neutral and a ground.
          I have four white wires coming out, presumably neutral. They are bundled and not connected to any of the switches.
          What would you like me to measure? I have one of those cheap voltage readers from Harbor Freight :-0



  6. I have an existing 2 wire Intermatic mechanical timer which is working fine for an outdoor incandesant bulb. I would like to install an LED bulb in the outdoor fixture. Are there any 2 wire in wall timers that will work with LED bulbs ?? Thanks for any help!

    • Hi Geoff,

      Hmmm, I don’t know the answer to that. LEDs are so new that a lot of the timer specs don’t mention LEDs. Can anyone else chime in?


  7. I have a 4-conductor digital switch that requires a battery from Westek. But I don’t think I have a ground, so I don’t think I’ll be able to tell you how it performed (confusingly, the old switch had a white and black wire attached)

  8. I want to install a timer switch for my pool light. When I examined the existing switch (inside the house) I discovered that the black wire leading to the switch from the pool is hot, I have a wall timer switch that I want to use. I don’t have a load wire to the light. What do I need to do to have this pool light on a timer. The hot wire leading to the light is 125. This leads to the junction outside and this is then step down to a 12v system for the pool light

    • Hi Larry,

      Sorry, I’m not familiar with pool lighting and wouldn’t want to steer you in the wrong direction.. Best consult an electrician.

      Good luck!

  9. I have installed a mechanical timer like the one pictured. It works fine during the day and turns on the light at the time selected. But then the timer just stays on, and stops advancing. I have eithher got a bad relay in the timer itself or the wiring is wrong, nut I don’t think it is. Any thoughts?

  10. I am getting ready to install the same timer you put in. I have a neutral wire, but apparently I do not have a ground wire! Is it OK to simply cap the green wire with a wire nut? L

  11. I have a covered deck with three different switches controlling the lights which I assume are two three ways and one four way. Can I install a digital timer on this circuit?

    • Hi Joe,

      I did a quick search and found a number of three-way timers available, but not any four-way timers. You might have to google around for that, if it is available at all.


  12. This article is wrong in stating that you cannot buy a 2-wire light timer that does not require a battery. I have an Intermatic mechanical, programmable light timer for an interior wall switch. It has 2- wires (both black) and no battery. It has worked well for years. The model is EJ351 and is available through Amazon.com To see the product details, go the Intermatic website. The installation instructions on the website show the two wires.

    • Hi Arthur,

      Thanks for the information! I stand corrected. I am surprised that this exists. I guess since the switch is purely mechanical, it doesn’t require the third wire. The only caveat to the EJ351 is that the instructions say it only works with incandescent bulbs, not florescent. Do you know if that is really true?


  13. Brian, I’m planning to install a digital timer because the old Intermatic mechanical timer we have makes a loud clicking noise whenever it turns on. Are there new mechanical timers that are make no noise at all when they click “on” or “off”?

    • The mechanical timer shown in my photo is pretty quiet.. I don’t even recall what kind of sound it makes, but it’s never bothered me. But, it does make some noise. I don’t know of one that is completely quiet.


  14. This is exactly what I was looking for! Glad I found your article. I’m planning to work on this project the next several days after buying the timer. I just have to figure out now if I have the patience to purchase online and wait for shipment, or get this directly at the local home depot (=


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