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.

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

The next choice you’ll have to make is whether to get a “mechanical” timer or a digital timer.

A mechanical timer 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, it’s more obvious how to program them. Here is the one I used (Jasco Products Company 15325 Indoor In Wall Timer).

Jasco Indoor Wall Timer
Jasco Indoor Wall Timer

This has been working well for me for years now.

When I first wrote this article, most digital timers, like the one on the below, were unreliable and ridiculously tedious to program (at least it was for me, and I have a degree in electrical engineering!)

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.

Since then, some better digital timers have come out that are much easier to program. I now recommend the myTouchSmart In-Wall Digital Timer because it’s vastly easier to program than previous digital timers, and it has great reviews online. But, be aware that it requires four wires.

This is an independent review site that receives compensation from the retailer or manufacturer (at no extra cost to you) when you purchase through the affiliate links on this site. I personally test and/or research each product or service before endorsing it. This site is not owned by any retailer or manufacturer. As an Amazon Associate I earn from qualifying purchases.

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

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