[How-To] How to retrofit-wire ALC switches


Senior Member
So, having now installed almost all our ALC switches, I decided it'd probably be nice to share some of the lessons learned, in the form of a how-to guide for taking existing 3 and 4-way switches and converting them to an ALC switch.

But first, a couple disclaimers:

  • You're working with electricity, which is DANGEROUS. If you're not very comfortable doing that, then don't and hire a professional to do it.
    [*]I am not an electrician, so the methods I suggest come with no guarantee that they're up to code, or even safe. They just simply worked for me. Use at your own risk.
    [*]Always always triple check the power is off before you start doing anything. I highly recommend those little testers that beep or glow when near high voltage.

Ok then. I won't go into how you replace a normal 2-way switch, because it's pretty much trivial. Connect the neutral, ground, hot, and switched hot, and you're ready to go. What this "guide" will do, though, is show you how to make 3 and 4-way wiring into basically a 2-way switch, so you can then replace that switch with an ALC switch. Besides everything you'd normally use to make electrical connections, you'll also need a continuity tester.

This guide also assumes you've already run your cat5 wiring to the gang box, and that it is sitting on top, just behind the sheetrock.

So here goes. I'm going to describe changing a 4-way switch (4 locations to control the light) because encompassed within that is how to change a 3-way too (since a 4-way light circuit has a 3-way switch on both ends). If you only need to change a 3-way switch, then just skip the parts below that deal with the 4-way switch.

1) Before you even pull the switch cover off, take a sharp pencil and make a very light line at the top of the cover. That will help you to know how far up from the gang box you can cut to get access to the cat5 wire, without causing a gap between the plate cover and the wall. Don't make too sharp a line, or the paint and paper of the sheetrock will easily peel away when you cut below it.

2) Remove the cover, and pull out the 4-way switch so you can access it. I like to take pics of everything in case someday when we sell I need to reinsert the old switches. So, stick a piece of tape on the wall for reference. Also, if there are multiple of the same color of wires, I like to put little marks on one of them so I can see in the pic where that wire goes.


3) (Making sure the power is off....) Unscrew all the wires, but keep them in their same basic orientation to each other. What we're going to do is connect the wires with wirenuts in the exact same connection as they currently are. That way, there's no fear that you're somehow connecting a hot directly to neutral, or other possible bad ideas. We're simply making permanent the connection that was already there, so you KNOW it's safe.

4) To do that, take the switch and use your continuity tester to see which screws were connected. Being a 4-way, that means the 4 wires were connected in pairs in some fashion.


Here we see that the left side wires were connected, and the right side wires were connected. So, go back to the switch box, and make those connections permanent. The remaining ground wire will be connected to your ALC aux switch.


Repeat this step for all other 4-way switches.

5) There should be 2 3-way switches left. One goes to the load, and one comes from the breaker box. Which is which? Dunno. Either way, decide which box you'll put your ALC switch in. Because of all the connections to be made, try to find a box it can go in that has a lot of room. In the other box (the one where an AUX switch will go), we're going to once again make the connection permanent that is currently there.

6) 3-way switches are different than 4-way and 2-way (duh!), but most notably because there are two "inputs", and 1 "output". That single output is called the common, and it should be very clearly labeled on the switch. It will either say COMMON in plain words, or at the very least be the different colored screw. If you're at all unsure which is the common on the switch, then use your continuity tester to see which screw makes a connection with both other screws, depending on switch position. For posterity and the possible eventual replacing of my ALC switches with the legacy switches, I label the common wire with a piece of tape marked "CMN".

7) So, pull out the 3-way, unattach the wires again keeping them in their respective locations to where they were, and then use the continuity tester to see which of the 2 screws is connected to the common wire.


In this case, the lower left screw is connected to the common (upper right screw). So, go back to the switch box and make that connection permanent. There's one wire remaining once this is done. Once all is said and done, this wire will be dead...but it's NOT a good idea to leave a bare wire in any switch box. So, put a wire nut on it, cut it short and cover with electrical tape....whatever you need to do.


8) Now we go to the last 3-way switch. This is where your ALC switch will go. So remove the cover, and pull out the switch. This is also the point where we're going to turn the power back on briefly. Why? First, to test that your connections so far have been correct. If so, then you should be able to turn the load on and off from this one remaining switch. Second, we need to figure out which is the hot and which is the switched hot wires.

Use extreme caution at this part. You'll have an exposed switch pulled out of the wall with high voltage going through it. Lock up the kids if you have to, and always be aware of where any metal is as you move around it.

9) Turn on the power and go to the switch. First, test that the switch really does control the load. If it does, the congratulations, you've made a 2-way switch! If it doesn't, then something got messed up somewhere, and I suggest hiring a professional. Now, turn the load ON. If your handy current detector is sensitive enough, you should be able to tell which screws are "hot". If it's not sensitive enough, then you'll have to use a multimeter to see which ones have 110V on them.

You KNOW the common wire will be one of the two wires carrying current when the load is on...so find out which of the other two wires has a voltage on them. Once you've identified which two wires have 110V on them, turn the load OFF. Check those two wires again. The one that still has 110V on it is the HOT wire, the one that now has nothing on it is the SWITCHED HOT wire. Double check....the switched wire should become hot again when the load is turned on. Mark the wire so you remember which is hot, and which is switched hot (I used an alligator clip for the hot).


10) Turn off the power again.

11) Remove the wires from the switch and make the correct connections for the ALC switch....ground, neutral, hot and switched hot. For the neutral, you'll have to pull out the neutral wires that should be connected together within the box and add the ALC switch wire to the group. Don't forget to put a wirenut on the single loose wire from the 3-way.

12) Screw the switch into the box, turn on the power, and confirm that it works. Congratulations!

13) Using the mark you made before, cut out a section of sheetrock directly above the gang box. It doesn't have to span the entire box. Using some really expensive tool....or a bent coathanger like I did...fish in there and find the cat5 wire and pull it out. Assuming you have enough spare, cut off any part that gets mauled in the process.


14) Make the appropriate wire connections. I suggest writing down the color combination and keeping it as a handy reference guide and above all BE CONSISTENT. Write all this stuff down or you'll lose track when you get down to the wiring closet.

15) Stuff the wires back into the box, threading the wires through the gap in the switch so they stay out of the way.


And you're done!

With enough practice, you too could have something that looks as safe and organized as this!

Very nice tutorial!
Bookmarked for 8 months down the road.

Do you have any pictures of the how the cat5 is sitting on top of the box pre-drywall? I would like to have something to show the LV and HV guy.

Also - after some use, how do you like the fancy wirenuts you have - better than the twist kind?
Ooops...ya, sorry Dan. Forgot there was a how-to. Please move it there.

Broccone, I had this pic laying around, not sure if it's good enough to help.


The main things are that it's clear from the front of the gang box so that the drywallers don't tear it to pieces using one of those rotozip tools they use to cut openings in the sheetrock with. But you also definitely want it loose enough to pull free. Originally I had looped the cat5 through the plastic on the top that holds the nail...but I was warned it was in the rotozip danger zone. so we pulled all those free and just stuck a loop on the top of the box with some electrical tape....just enough to hold it in place, not enough to secure it. I'm glad I did..it would have been a lot harder to get the wire out if it had been looped through the plastic.

Just make sure you leave a lot you can pull out, and if your cat5 runs to multiple boxes nearby, make sure you secure it between so you don't pull it off an adjacent box when you pull it out of the wall.
I definitely like the wago lever nuts, which I discovered thanks to TonyNo. They're not exactly cheap, so I won't use them for everything...I mainly got them for the ALC stuff.

The things I like about them are that they handle stranded and solid easily. I know I've used regular wirenuts for that, but I have less concern about it coming loose with these. The other thing I like is that you can handle one wire at a time....makes making the connections a lot easier than trying to line up the wires just right to get them into the nut. And you also get a do-over with these, in case you find you've connected some wires through each other....just open the lever, untangle the wire, and reconnect. That's probably one of their biggest advantages.

That being said...again, they're expensive compared to wire nuts...but probably don't qualify as "expensive". It's also hard to say if they take up more room than the LARGE wire nuts...but they're definitely not flexible like those are, so if your gang box space is already tight, these may not help.


I like them for this purpose, especially since I can imagine a scenario down the road pulling these switches out and replacing with the old switches when it comes time to sell.

I found that when tryign to replace the old switches and having the ALC switches partially connected and dangling around my walls were gettign scraped up. I ended up taking a ktichen towel and sticking it on the bottom of the gang box and having it drape down the wall so the switches etc scrape up against it.

Got my first ELK<>ALC controlled light working last night, no real issus.

Have not tackled a 3-yet but it's coming this week.
When i was thinking about it, one coudl just grab all 4 wire coming in to a 4 way switch and wirenut them all together, same with the 3 way.

On a 4 way or a 3 way there really is no 'hot' since either the black or the red can be hot depending on which position the switch is on. I guess I'll be sticking some ductape on with the light name and the HOT or TRAV. Hopefully the color usage will be consistent (red for travellers) so I will only need to label the wire with the light name.

While this woudl work, converting it back to a non ALC setup could be a pain since you wouldnt know which wire is which.

I noticed the grey LV wires on your dimmer, in my case that is the green and is the AUH-ON signal wire. How old is that switch?
When i was thinking about it, one coudl just grab all 4 wire coming in to a 4 way switch and wirenut them all together, same with the 3 way.

I guess that's true. However, when you get to the last 3-way switch, how will you know which is the hot and which is the switched hot? You won't be able to use the method I described, since both positions on the 3-way will have power on them (essentially, you'll have hardwired the load to On). There's probably still a clever way to figure it out, but I don't know what it is.

I agree that going back later and seeing all of the wires nutted together might make for some difficulty unravelling if you have to.

On a 4 way or a 3 way there really is no 'hot' since either the black or the red can be hot depending on which position the switch is on. I guess I'll be sticking some ductape on with the light name and the HOT or TRAV. Hopefully the color usage will be consistent (red for travellers) so I will only need to label the wire with the light name.

I had reds, whites, and blacks on my switches. There was no pattern that I could see, as to what was a traveler and what was hot, etc.

I noticed the grey LV wires on your dimmer, in my case that is the green and is the AUH-ON signal wire. How old is that switch?

Oh, for all I know, that's the NEW coloring scheme. All other of my switches, the aux on is green...that particular one, for some reason, it came as grey, and also with a little notice note in the box that the aux on wire was a different color. So either they put that notice in older boxes so it wouldn't conflict with the new (green) color scheme, or grey is the new green!

On my first relay I got, one of the ALC control wires is actually purple. I think it's the "white" one. That caused just a bit of confusion when going through the docs to hook that up....