As marked before from the original switch, one wire (either power in, or the wire to the light fixture) goes to the black terminal, two wires go to the brass screws, and the bare copper wire (not visible here) goes to the ground screw.
What is the black screw on a light switch for?
The black screw has the black (common) wire that runs up to the light through the yellow cable. The two grounds are connected together and then to the green ground screw on the switch. To summarize, the black screw gets either the wire from the electrical panel or the wire going to the light.
Where does the black wire go on a switch?
When you turn on a light switch, power goes to the light through the “hot” (black) wire and then back through the neutral (white) wire to the ground. The bare or green-wrapped ground wires serve as a backup to divert the power safely away in case of an electrical fault.
Does it matter which black wire goes where when changing a light switch?
With a switch loop yes, it should. The hot wire should come down from the ceiling on the white wire and go back up on the black wire. Just think white down, black up. If you wired it the other way around, hot black down and hot white up, you have a problem.
What wire goes on the common screw?
hot The most important wire to get right is the one connected to each switchs common screw terminal. This is the hot wire (usually colored black, but not always), and it brings the power from the source and delivers it to the first switch and then from the second switch to the light fixture.
Does the hot wire go to the black screw?
The white (neutral) wire connects to the silver screw, or you place it in the back wire hole on the same side of the device as the silver screw. The black (hot) wire goes to the brass screw or into the hole in the back of the device on the same side as the brass screw.