Network cable testers are basically a battery and several lights, with the network cable itself providing the current path. If the cable is good, the bulbs will illuminate. Making one of these at home can take the average person about fifteen minutes.
Cut the working network cable so that there is more than a foot of cable to each capped end. The clear adapter caps will allow it to be plugged into a networking socket, and they can be for CAT-3, CAT-5 or any variant.
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Strip the wires on both of the working network cable's cut ends, and separate the wires by color. There should be two types for each color, one solid and one striped. These will serve as the positive and negative leads for the light bulbs.
Connect the ends of one stripped cable to each of the light bulbs, using the solid wire for the positive terminal. There should be half as many bulbs connected to the cable than wires in the cable; if there are eight strands in the cable, there should be four lights. If the desired tester is to be used on capped network cable itself, then the female wall plug adapter can be connected to the stripped wires. It has screws in the back that will accommodate eight wires, or four paired connections. Once splicing is complete, wrap all connections with a liberal amount of electrical tape, to prevent them touching each other or grounding out.
Connect the solid colored wires of the remaining stripped length of cable to the battery's positive terminal, and the striped wires to the negative terminal.
If using the female jacks, connect the wires from a second female adapter to the positive and negative terminals on the battery, as described above.
When the cable with lights is plugged into a network jack (or has its jack plugged with a cable), and the battery's adapter is plugged into the terminating lead of that jack or cable, the lights will illuminate for each pair of wires in the cable. If one or more lights do not light up, then the cable could be bad.