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I'm a home DIYer and have some familiarity with electrical work. I recently bought a home and am replacing the switches. In the upstairs hallway, there are 3 switches that control one light. After researching online, I learned that this should be handled with two 3-way switches and one 4-way switch. However, it looks like my setup has one 3-way switch and two 4-way switches (see pictures). The house was built in 1985 and am fairly confident there is not a fourth switch. Can anyone explain why this was setup this way or what I have wrong?

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  • Can you post photos of the insides of the light fixture box? Aug 3 '20 at 3:55
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    Maybe there was once a fourth switch? Any blank wall plates around?
    – DoxyLover
    Aug 3 '20 at 4:06
  • 4th switch. That is absolutely clear. By the way, this is conduit where the installer has a choice of 8 different hot colors... and what you see is exactly how I wire 3/4 ways, except I use 2 yellow instead of 2 orange. Same concept though. Aug 3 '20 at 6:19
  • @DoxyLover was correct. I found the mystery fourth switch on another side of the house. Thanks for making me reconsider my assumptions!
    – kgb0716
    Aug 4 '20 at 3:28
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In the comments, I suggested that there may have previously been a 4th switch and to look for a blank switch plate somewhere.

The answer was that there was actually a 4th switch (2nd 3-way) elsewhere in the house.

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A 4 way can be used as a 3 way, you just have to connect travelers to common colored screws, and attach the common wire (the hot or switch leg) to one of the other screws leaving its matching screw empty.

But seeing all terminals have wires this does seem unlikely. It would mean a fourth wire is uselessly connected to the switch and goes to the light unused or that it was routed to another junction box where another switch was intended but not installed.

You could test by removing one wire at a time from 4 ways looking for the wire that has no effect. Permanently insulate that wire and connect the wire it travels with to the common on the new 3-way. (If you do later find a mystery hidden three way it will act like a kill switch, only allowing the other switches to function when it is in the closed position.)

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  • Indeed, "pernamently insulate" is proper, for unused wires. Don't leave mystery wires that are possibly live unconnected. Preferably insulate it on both sides, but I suppose that's part of the issue here!
    – P2000
    Aug 3 '20 at 15:17

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