Interpreting a junction box

Old 05-28-16, 12:55 PM
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Interpreting a junction box

We're installing some new light fixtures and in the process we discovered that one of our junction boxes has wiring that doesn't make sense to us. Can someone help me understand why the box is wired this way? Here's the info:

1) The box has two switches. The first works just fine, is connected to a two-wire-with-ground cable. No problem there. (it controls a two outlets and two lights in a hallway).

2) The second switch doesn't seem to do anything. We've tested it with all the outlets (yes, both top and bottom plugs), etc. and it's still a mystery. Here's how it's wired:
There are two different cables connected to this switch:
Cable A is a two-wire-with ground cable. The white wire from this cable is capped/twisted together with the black wire from Cable B. The black wire from Cable A is connected to the switch.
Cable B is a three-wire-with-ground cable. The white and red wires from this cable connect to the switch. As mentioned above, the black wire from this cable is twisted onto the white wire from Cable A.
I'm a complete novice. What is going on here? Any help is much appreciated!
Old 05-28-16, 01:07 PM
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Welcome to the forums.

You are dealing with a three way switch. There should be a mate to it somewhere.

You should have three wires on the switch. The wire on the black/dark colored screw is the common wire.

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