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I have few questions here. Hope you have the answer for it.

1: Is this your new home? (Call the builder if answer YES)
2: Is this a house you just move in? (Make sure it is something wrong before makes any wiring change)
3: Was any wiring change by someone or yourself? (Do you remember what has change?)
4: These wiring will not change on its own, try to remember what you have done recently.
5: The light that controlled by the 1st switch. is it also controlled by a 2 second switch?(one light can on/off at two different location?(most of the house, the light for the hall way is controlled by two 2 way switch, it is convenience turn light on when you come home. and light can be turn off after walk in the middle of the house.

Base on what you said. There are two possibilities
#1 : The Red and the Black wire are two different phase that come out from the main panel, black used for the light, and the Red just pass though the junction box then feed to other light switche or out let.

#2: The Red is a back feed to or from the second 2 way switch. (One light can switch on/off from two locations.)

By the way. My home have a switch at the door entrance, works exactly the same as yours. One switch turns on/off my living room outlet. And one light as well.更多精彩文章及讨论，请光临枫下论坛 rolia.net