PAIZA99 If you spot any of these symptoms of switch failure, install a replacement wall switch as soon as possible. With cover plate removed, you'll see two screws holding switch in switch box. It has been claimed that there is a constant scale factor between the two coding methods, and that allowance can be made for this. How can I unlock my front door when I'm out of town? Three-way switches allow you to turn light on and off from two different locations, such as at top and bottom of stairway. Look carefully at three terminal screws; you'll see that two are one color while the third is a different color.|Need to Rewire a Lamp?