Sometimes a phone line loses the jack plug from one end or the other, and it has to be replaced. The other telephone wiring situation that leads to plug installation is the cord for an older phone that comes with a modular phone jack plug on one end, but has spade terminal hooks on the other. In either case, a plug is easily added to the phone wiring with a crimping tool, so it can work with a modular telephone jack.
Strip the outer cable away from a phone line with the stripper on the crimp tool. Some crimps have flat cable strippers, and some will strip both flat and round, while others do not have a stripper for either. Use a utility knife carefully to slice the outer jacket lengthwise if the crimping tool does not have a stripper that works on your phone wiring. Cut away 1 inch of the outer jacket without snipping off any insulation from the inner phone wires. The small inner wires do not need stripping.
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Cut the spade terminals off an older phone cord with wire cutters. Cut the four colored wires to a uniform 3/4 inch length.
Hold a modular telephone jack plug with the front of the plug facing away and the clip facing down. Designate a number for the four holes in the back, starting with number 1 on the left and ending with 4 on the right.
Push the phone line wires into the holes with the standard wiring color code. Push the black wire into hole 1, the red wire in hole 2, the green wire in hole 3 and the yellow one in hole 4. Forcefully push the wires into the plug as far as possible.
Use the new telephone wiring color code for adding a plug to a newer cable. Push the white wire with orange stripes into hole 1, the blue with white stripes in hole 2, the white with blue stripes into hole 3 and the orange with white stripes in hole 4.
Check the phone wiring color code in the plug to be sure the correct colors are in the correct slots. Crimping is permanent, so afterward the wire positions cannot be changed.
Push the wires into the end of the plug and hold them firmly in place while clamping the jaws of the crimp around the plug. Squeeze tightly on the handles of the crimping tool to ensure a good connection for all the telephone wiring. Pinch the clip and plug the crimped plug into a modular telephone jack.