I want to change out some 3-way light switches in our 40 year old house and will have quite a few questions by time it is done. The switches and wires aren't marked and are not standard colors. There seem to be more wires between the switches than I expected ( i.e. 1 common coming in to the switch, 2 travelers out,etc.)

The first general question is that the common screw is not marked and all the screws are all copper on the existing switch. 1) How can I figure out which wire is the common wire?

With the circuit tester light up with the switch off and by touching the common and the box? Does this indicate anything?

Thanks for helping to get me started

 

A continuity tester is needed here. A continuity tester (aka ohmmeter) is a standard part of any multimeter.

Carefully mark the three wires connected to the switch as to which screw they were connected to. Then remove the switch, without disconnecting anything but those three wires.

Put the switch on a table. Examine the back of it carefully. Often, you will find the letters "COM" or "COMMON" on the rear of the switch case.

If not, the common screw will be the one that has continuity with the other two screws alternatively depending on the position of the switch.

 

Thanks. It looks like I'll be buying a new tool.

Next question:

The two switches that I am trying to change are located 1) at the bottom of the stairway and 2) at the top of the stairway with the light fixture located past the stairs and in the middle of little foyer area.

A Red and White(Off white,pale, not really white) wire enter switch #1 from above the switch. The white wire enters and exits the box with connecting to the switches.

The Red wire raps around the bottom left screw on switch#1 and then connects to the top left screw on switch# 2. This wire on switch #2 always had current.

A yellow wire runs from the top right screw on switch #1 and wraps around the bottom left screw on switch#2 and exits the box with the white wire.

A blue wire connects the top right screw on switch#1 to the top right screw on switch#2.

Why are the wires wrapped around the screws and then sent rigth back out of boxes? I would have thought the wiring would have been something like red in and yellow and blue out to switch2. From switch 2, 1 independent wire going out. The screws unscrewed from the old switches, but on the new switches, the screws didn't seem to want to come out. Should they unscrew all the way? I don't want to have to cut the wire,strip it and then try to get to wires (or the two pieces of the same wire) connected to the screw.

Enough questions for now. Any insight would be appreciated.

 

You listed two wires connected to the top right screw on switch #1, and no wires connected to the top left screw on switch #1. Can you revise?

You also don't say anything about how the three white wires are connected. Can I assume that they are all connected to each other?

You have described two switches in the same box. Are these at the top of the stairs or the bottom of the stairs? Does switch#1 or switch#2 control the light in the foyer? What does the other switch control?

Finally, do you live in the Chicago area?

 

You listed two wires connected to the top right screw on switch #1, and no wires connected to the top left screw on switch #1. Can you revise?

Should have been: A yellow wire runs from the top LEFT screw on switch #1 and wraps around the bottom left screw on switch#2 and exits the box with the white wire.

You also don't say anything about how the three white wires are connected. Can I assume that they are all connected to each other?
The white wire bypasses the switches, but is connected to the light.

You have described two switches in the same box. Are these at the top of the stairs or the bottom of the stairs? Does switch#1 or switch#2 control the light in the foyer? What does the other switch control?
One switch per box. Both switches control the light and nothing else directly. There are no outlets or other lights in the area that are controlled by the switch.

Finally, do you live in the Chicago area?
Minneapolis

 

Are you making some unstated assumptions? When you say something like "a yellow wire runs from the top right screw on switch#1 and wraps around the bottom left screw on switch#2", do you mean that you can actually see the yellow wire for the entire run between switch#1 and switch#2? Or are you assuming that since there is a yellow wire in both boxes, that it must be the same yellow wire?

 

I am making some assumptions since the stairway is only 5 stairs, and the exit from switch # 1 is on the middle right side and the entry into switch#2 is on the middle left side.

 

I drew this out on paper, and I've been staring at it. But it makes no sense. I suspect that one or more of the assumptions that you made about what is going on behind the wall is incorrect.

It seems logical to assume that the bottom left screw is the common on each switch. That means that the red wire is the constant power, and the yellow wire is switched power to the light (or possibly vice versa). But I can't figure out the rest of it.

An examination of the wiring at the light itself seems to be the next logical step. Also, take my earlier suggestion and conduct a closer examination of the switches to see if there are any markings on the back.