This is known as "staircase wiring". It uses two two-way switches. A two-way switch has one common terminal and two alternate switching terminals. Say C1 being common, A1 and B1 are alternate terminals. second two-way switch has C2 common terminal and A2, B2 alternate terminals. Connect the live phase wire to C1. Wire up A1 to A2 and B1 to B2. Connect a load (say a lamp) to C2 and the other end of the lamp to neutral. The wiring is complete and now the lamp can be controlled by these two switches.s for USA, Canada and countries using similar 60Hz mains suppliesIf this is a standard 120V light fixture controlled by two light switches, for more information, including a wiring diagram, see the Related link shown below.
If, and ONLY if, there is an on/off switch for a 120 Volt lighting fixture installed onto a wall box containing wires, it is possible that the Red and Black wires in this situation are:
a) the "hot" feed wire coming from the mains breaker panel to the switch and
b) the "switched hot" wire going to the lighting fixture.
BE VERY CAREFUL: YOU MUST BE SURE YOU UNDERSTAND
HOW TO DO ANY OF WHAT FOLLOWS SAFELY BEFORE YOU TRY TO TEST ANYTHING WHICH MAY BE A HOT OR LIVE WIRE
Only someone who knows how to use a test lamp or voltmeter safely will be able to confirm if the Red wire in the wall box is a) and the Black wire is b), or if they are actually wired the other way round, meaning the Black wire in the wall box is a) and the Red wire is b).
A Red wire can be the first "Hot Leg" of a 240 volt supply. It could also be one of a pair of hot wires connecting two switches controlling one or more 120V lighting fixtures.
A Black wire can be the second "Hot Leg" of a 240 volt supply or the "Hot" wire of a 120 Volt supply. It could also be one of a pair of hot wires connecting two switches controlling one or more 120V lighting fixtures.
A White wire is normally the "Neutral" wire. It is common to both hot legs on a 240 Volt supply.
A Green wire (or bare wire with no insulation) is normally the local "Ground "wire.
As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.
Before you do any work yourself,
on electrical circuits, equipment or appliances,
always use a test meter to ensure the circuit is, in fact, de-energized.
IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB
SAFELY AND COMPETENTLY
REFER THIS WORK TO QUALIFIED PROFESSIONALS.