Replacing an old 3 way switch with a new one

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Old 03-23-17, 07:01 PM
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Replacing an old 3 way switch with a new one

I'm hoping for some guidance with a recent problem I'm having...

Recently a light switch broke in my kitchen. The light is switched from both ends of the room. My problem is that the switches are so old that they are not labeled, nor are the screws colored differently. The house was built in the late 50s so the wiring is all BX, and no ground wire. It's not clear in the pics, but the switch says "A-H&H" on the toggle and stamped on the chassis.

So here's what I've got going on: There is a black wire on top with a white wire, and a red on the bottom. When the lights are on (it's a ceiling fan), i have 64V A/C from the black to red, and also from black to white. With the lights off, 120V from black to red, and black to white. The white and red wires have continuity regardless of whether or not the light is on.

The goal is to replace this broken switch with a modern 3-way but I'm not 100% sure which wire is considered common (black screw) and which two wires go to the brass screws.
 
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Old 03-23-17, 07:07 PM
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Try the black to the common and test. Be sure to try the other switch also.
 
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Old 03-23-17, 07:13 PM
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Yes, I should have mentioned that... the only reason this light is still operational is because I was just using the other switch.
 
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Old 03-23-17, 07:17 PM
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If the wires are transposed the one switch may only work the light's when the one switch is in a certain position.
 
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Old 03-23-17, 07:46 PM
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Yeah that's exactly what's happening now. Just hooked it up.
Both switches have to be "up" now in order for the light to turn on. Before, the light would turn on when either switch was up. Is there a way to change this?
 
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Old 03-23-17, 07:59 PM
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Now try using white as the common and black as a traveler.

Nothing will spark or short out if incorrect.
 
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Old 03-23-17, 08:03 PM
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I will give that a try after work tomorrow.
Thanks guys.
 
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Old 03-23-17, 08:10 PM
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You may end up trying the third wire as common.

When finished..... note which two are travelers so that you know for the other end for when that switch needs replacement.
 
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Old 03-24-17, 02:48 PM
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Third time was the charm. The red wire was common. So now if anyone in the future has an AH&H 3-way light switch, and this thread comes up in a search, the bottom terminal is common.

Nice to see they wired SOMETHING in this house properly.
 
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Old 03-24-17, 03:24 PM
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the bottom terminal is common.
A 3-way switch doesn't have a top or bottom. They can be put in either end up. Was there by chance a letter "C" embossed on that end?
 
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Old 03-24-17, 03:26 PM
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Thanks for letting us know the outcome.

The biggest problem is there no standard to where the C terminal is located on the switch.
Because of that very reason they started using a universal identifier.... a dark colored screw for common.
 
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Old 03-25-17, 10:52 AM
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A 3-way switch doesn't have a top or bottom. They can be put in either end up. Was there by chance a letter "C" embossed on that end?
I just replaced several original 3-way switches in a 1950s built house for a family member. I was amazed when I looked closely at them that there was absolutely no "C" or "Common" marking on them at all. That leads me to wonder how an electrician in the 1950s knew how to connect the switch.
 
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Old 04-16-17, 05:47 PM
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Thank you for this thread! As someone who has absolutely no knowledge of things electrical, I decided to change out the old 1950's 3 way light switches in my house. I ran into the problem of them no longer functioning properly after I put in the new switch. Three wires, one red, one black, one yellow. I put them in the exact same location as they came off the old one, but no go. Finally figured out the yellow is the common and the black and red are the travelers. I'm guessing the switch was put in upside down as the common wire was top left, rather than on the bottom. Since there are no markings at all on the switch and all the screws are the same color, I also wonder how they managed to install them in the beginning!
So thanks to this thread, problem solved. I would never have figured it out other wise!
 
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Old 04-16-17, 06:01 PM
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I'm guessing the switch was put in upside down
No such thing as upside down and it was probably a white not yellow wire but you got it that is the important thing thing. Glad we could help.

One common can easily be found by looking for where the power in hot is connected. Assuming both switches are identical then it also tells you which is common on the other switch. Even if the other switch is different you probably now know the color of the travelers on the other switch so you can guess the common location by elimination. Of coures K&T all bets off.
 
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