Things You'll Need
RJ11 jack (either wall or surface mount)
In the 1960s, the standard telephone connector was a rather large plug with four protruding prongs on the phone cord, which plugged into a wall-mounted jack. Today, the standard phone connection for basic homes and small businesses is the "RJ11" modular plug and jack system (the "plug" is the male connector and the "jack" is the female connector). These plugs and jacks are much smaller and lighter. In an old home or building, you may run across a four-prong jack, which you can easily convert to a modern RJ11 jack.
Unscrew the four-prong jack box from the wall or whatever surface it is mounted on.
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Unscrew the four wires bundled in the cable coming in from the outside line.
Select an RJ11 modular jack from your local electronics store. They come in small surface-mount units (typically mounted on a baseboard) and ones that fit into a standard electrical outlet box for mounting on the wall.
Match the four color-coded wires to the color-coded screws on the RJ11 jack. The screws themselves may not be color-coded, but you will see colored wires attached to the screws that are wired to the RJ11 jack connector. The red and green wires are for line one. If you have two different phone numbers, the yellow and black wires will be for line two.
Using a pair of needle-nose pliers, bend the end of each wire to form a U and position it around the color-matching screw's post. Tighten the screw with a Phillips screwdriver. Do this for all four wires.
Mount the jack on the wall or baseboard with the provided screws, or if you purchased a wall-plate jack, screw it into the existing electrical box.
Insert the modular connector plug from your telephone into the jack and push it until you hear a click. Your phone is now operational.
If you do not want to replace the four-prong jack, adapters are available (from such local sources as RadioShack) that plug into a four-prong jack and have an RJ11 jack built into them to accept a modular phone plug.