You set out to replace one or both switches in a two-switch
light circuit. You cannot remember how they were wired, and now
things do not work. If your light circuit has three or more
switches, see instead My 4-way switches don't work. What do you
do? First, you may find it helpful to understand how 3-way
switches work to accomplish this task. See Tutorial: How 3-way
and 4-way switch circuits work. Further, this discussion assumes
that you have only disconnected the switches and have not
removed wire nuts of any other connections inside the switch
boxes. Note that there is a 3-way switch at each end of your
circuit. We need to answer the following questions: You
generally need two people working together answer these
questions: one with the meter on resistance, one tapping pairs
of wires First, kill the circuit breaker and be sure there is no
power to the circuit. Next remove both switches. To answer
Questions 1 and 2: Post person A at the first 3-way box and
person B with the meter at the second 3-way box. B