Old Wire, New Switch

It can be difficult working with the deteriorated knob-and-tube wire ends inside a box. You might have to snip off the end, and the remaining wire can be a little too short to easily connect to a new switch or receptacle. In this case, you can pigtail a short, new piece of wire to the existing wire and connect the pigtail to the terminal screw on the device. This also will bring the wires into compliance with the NEC, which calls for six inches of workable wire length inside a box. The following diagram shows this type of pigtail.

Dimmers

You can replace any interior single-pole switch with a dimmer if the box is large enough to accommodate the larger body of the dimmer. Don’t try to pack it into a tight or overcrowded box because this is a fire hazard (see the instruction sheet that comes with the dimmer). Dimmer switches come with about four inches of their own wiring or lead wires (line and load and ground wire) ready to connect with cable from the circuit with wire nuts.

The Great Outdoors

You cannot replace an outdoor switch with an indoor switch unless you also use a bubble-type cover or a cover with a flip-style lid. These are weatherproof covers. Better yet, you can use a cover with a built-in, horizontal, lever-type switch that comes with a foam gasket between the cover plate and the box. The lever activates a regular toggle switch underneath. Other than that, the replacement procedure is the same as a regular single-pole switch.