Replacing a 3 way switch (controlling a light or outlet from 2 different locations) is a little tough for first time DIY's, but with the following instructions you should be able to replace the switch yourself. Always remember to turn off the power before attempting any electrical repair.
Determine which switch is not working. You do this by turning each switch on at both locations. With the light on, go to each switch and flip switch to opposite position. The switch that turns the light off is the good switch. Replace the other switch as follows...
First shut off the circuit breaker or fuse that controls the light. You can have a second person flip the breakers while you watch the light go out. (If you are controlling an outlet, plug something into the outlet.) If no second person is available to help, then you will have to shut off breakers yourself by looking at your power panel (hopefully it is labeled) and start turning off breakers until the light goes out.
Now remove the switch plate cover and set aside. You will then be looking directly at the switch. See Figure.
After verifying that the circuit is off, use a screw driver and remove the mounting screws at top and bottom of switch. Pull the switch straight out toward you as far as you can. Do not try to pull switch beyond the length of the attached wires.
Remove the wires from the top two screws at the top of the switch. Separate them and then remove the bottom wires and separate. (Push right wire to the right and left wire to the left.) The wire on the bottom left side is the ground wire and should be gray or green in color. The wire on the bottom right screw is the power lead from the electric panel. This wire should be black, but could be red. See second figure.
Open the package of the new 3-way switch. It should look similar to the one pictured above. It should have 4 screw terminations -- 2 at the top of the switch and two at the bottom. The screw on the left will be smaller and lower on the left hand side of the switch. If it only has 3 screws, it is the wrong switch.
Take one of the two wires at the top of the box (if you start with left side, then use the wire on the top left side), unscrew the top left screw and insert the wire behind the screw. Make sure the end of the wire will wrap around the screw in a clockwise fashion, and tighten the screw. Be sure to tighten all screws. Going in the clockwise fashion prevents the wire from working loose as you tighten it.
Repeat this procedure for each of the remaining wires. Make sure to keep wires on the proper side (as you left them when you removed the old switch) and that the hot (black/red) wire goes on the bottom right side. Also make sure that the bottom left wire goes on the ground wire screw.
Reinsert the switch back in the wall box. Make sure that wires are all safely returned inside the box and no bare wire ends are touching anything other than the screws they are mounted on. Put the retaining screws back in the box and tighten.
Mount the cover plate and test the switch.
Hope this helps!
Ron has been a licensed Real Estate Salesperson, Licensed electrician, Director of Finance for a local non-profit, Systems consultant for Ameritech and Digital Equipment Corporation. View more detail at: