Wiring 3 way switch

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Old 01-22-17, 04:08 PM
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Wiring 3 way switch

I decided to update my switches in my house to some more modern white switches. I have a 3 way switch in my living room at the staircase. There is another switch at the top of the stair case and they both control the light at the top of the staircase. I only replaced the one downstairs. There were 3 wires, two black and one red. The red was attached to the black screw. On the new switch, I attached red to black and then the two black wires. Neither switch worked. I reversed the two black wires and now the switch upstairs works. The downstairs switch only works when the upstairs switch is on. When the upstairs switch is off, the downstairs doesn't work at all. I'm really not sure what I need to do to make these switches work properly.
 
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Old 01-22-17, 04:22 PM
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Welcome to the forums.

A three way switch always has one marked screw terminal. It is darker or black compared to the other two. That is called the common wire. Whichever wire comes off the common terminal of the old switch MUST go on the common terminal of the new switch.
 
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Old 01-22-17, 04:23 PM
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I only replaced the one downstairs. There were 3 wires, two black and one red.
Assuming cable not conduit here should have been a 3-conductor cable with a white wire, a black wire and a red wire. Please tell us all the wires in both switch boxes.
 
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Old 01-23-17, 07:16 PM
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That's the thing, there was no white wire. I could only see two black and one red wire coming out of the conduit. The red wire was on the black terminal of the old switch and that is what I put it on the new switch.
 
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Old 01-23-17, 07:37 PM
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You could try to switch the wires on the common. You will find the correct connection in two tries or less.
 
 

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