Home telephone wiring is not very complicated, despite the collection of wires in a bundled cable. It takes just two wires to make a connection, so if your phone isn't working, you just need to trace along these wires to find where the connection is broken. The wires are colour-coded, which makes finding problems easier. A test phone is a good tool to have when you are looking for problems in your phone line. Because it doesn't need to be plugged into a wall outlet, you can use it to check for a dial tone at any jack.
Open the door to the network interface device (NID) with a Phillips screwdriver. It is located on the side of your house just below where the phone company lines drop down. There are a series of modules inside, each supplying one phone line. Each line is identified by the telephone number on the door of the module.
Remove the plug from the jack just under the module for the phone line that isn't working and plug in a test phone. Listen for a dial tone. If you don't hear one, or it is weak or scratchy, call the phone company. The problem is in their lines, and it is their responsibility to fix it.
Unscrew the green and red terminals inside the module, take off the attached wires and inspect the ends to make sure at least 1/2 inch of bare wire is exposed. Strip off more insulation with a utility knife if there is less than this.
Note the colours of the wires connected to each terminal. If you have only one phone line, the phone company standard is to use the red/green pair, or the pair with blue and white stripes. If it's a second phone line, the standard is to use the yellow/black pair, or the pair with orange and white stripes. The red or yellow wire, or the one that has a solid colour with white stripes, should be connected to the red terminal. The green or black wire, or the one that is white with solid stripes, should be connected to the green terminal. Follow this standard to avoid confusion when checking the connections in the jacks in your house.
Plug the test phone into the jack in which your phone is plugged. You may have resolved the problem by tightening connections at the NID. If not, unscrew the cover of the jack, remove it and check the wiring. The wire connected to the green terminal in the NID should be connected to either the green terminal in the jack, or the one with a "T," for "tip." The wire connected to the red terminal should be connected to the red terminal, or the one that says "R" for "ring."
Connect the wires to the two central terminals, if the jack has room for more than one line, and you only have one phone. Make sure the wires are sufficiently stripped, and that the connections are tight.
Test the line again with the test phone. If the problem persists, trace along the phone line from the jack to the NID, looking for signs of damage. Mice and rodents sometimes chew through telephone cables. If you find damage, screw a wiring block, which is a junction box for phone wiring, to a nearby stud, cut the wires and attach each end to the terminals on the block, keeping in mind the colour code you are using.
Check the wiring between jacks if the dial tone is good in one phone, but scratchy in another.
Sometimes signal problems are the fault of the phone itself. Make sure your phone is plugged in. If it is a headset, be sure the battery is charged. You don't have to follow the standard colour codes for phone wiring to make your phone work. If you do follow it, though, you will save confusion for yourself and anyone else who works on your lines.