You posted under 3-way switch.
Example of 3-way switch is a hallway with switch at each end of hallway.
If you have a different switch, then instructions below do not apply, so add a comment.
1) Your old switch has 3 screws: 1 dark screw and 2 brass screws.
New switch has same color screws.
If you can remember where wires went on old switch, then re-connect on new switch using color-coded screws.
This is why I learned to make notes or take a photo before disconnecting electrical device.
2) If you are uncertain where wires went on old switch, then we can test.
The testing takes more words than it does work, and it will resolve problem.
You are replacing one 3-way switch, but other 3-way switch is still in the wall and is wired correctly.
We will call the other switch: switch2
Move switch2 to down position.
Separate wires at new switch for testing.
Use ordinary two wire tester.
Tape tester leads to wood to keep hands away from power
Turn power ON.
Test each wire to bare ground wire.
Tester lights up on Hot wire. Mark this wire.
Now move switch2 to up position and repeat test.
Tester lights up on Hot wire so mark this wire.
>If same wire is Hot in each test, then this wire connects to dark screw. If this wire was also connected with another wire on old switch, then connect that other wire to brass screw also.
>If two different wires tested Hot, then these are the travelers, and each traveler connects to a brass screw. One traveler on one brass screw and other traveler on other brass screw, in any order.
Leave switch2 in up position. One wire is Hot and has power.
Test this wire to all other wires in box, except bare ground wire.
Tester lights up on Neutral wire(s). This wire(s) is not used in the 3-way circuit, so put a wire nut over Neutral.
Add a comment for more free help.
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