Black wire always to negative terminal DC Battery Connections White wire always to positive terminal
DC Connections Black wires identify negative or hot wires. Switches connect on negative side of battery to the load (light). White wire is used to identify the positive polarity. Black Switch White
Black This Knife switch shows black wire in and black wire out.
This type of miniature lamp socket has a brass colored screw and a silver screw. Black wires will connect to brass and white wires connect to silver.
Red wire is also like black and can be used to identify the negative side or switch side of a circuit.
This is a 3-way circuit. Red and black wires are used to identify the path of current and are on the negative side. Red Black White Black 3-way switch
Black This is a 3-way/4-way circuit. Red and black wires are used to identify the path of current and are on the negative side. The lights are in series. The black wire in between the lights could also be red. 4-way switch
Common Wire for AC Type 1 Romex Cable 2 conductor with a ground Black Ground White
Common Wire for AC Type 2 Romex Cable 3 conductor with a ground Ground Black Red White
Ground green terminal AC Connections Wiring an Outlet White silver terminal (neutral) Black (hot)
Outlet other side: Black wire on brass terminal (hot)
AC Connections Wiring a Switch Ground green terminal Black (hot) Neutrals tied together
AC Connections Wiring a 3-way switch Wiring of a 3-way switch using 3 conductor Romex cable. This is an exception where white can is terminated on the switch and is a HOT (live) wire!
A closer look a the 3- way switch. Notice the dark screw, that is the common position.