Do not be disheartened..when installing the self wiring switches and plugs on ZIP Cord, if at first you don't succeed, your running about average.
ZIP CORD is the proper name for the light guage molded two conductor wire that is commonly used for lamps and small appliances. (It gets the name Zip cord because once you separate the conductors you can split the wire like pulling a zipper).
As with all wire, zip cord is rated by the size and ampacity of the electrical conductors and is indexed by the American Wire Guage (AWG) standards.
Zip cord is commonly available in sizes AWG 12, AWG 14, AWG 16 & AWG 18. AWG index is a fraction of an inch therefore the larger the number the smaller the wire, and therefore the larger the number the smaller the load the wire can carry. Lamps will typically use AWG 16 or AWG 18 while the AWG 12 & AWG 14 is typically used on small appliances such as a Mr.Coffee type coffee maker or a small hand held food mixer, however, some lamps such as a swag lamp that has numerous lamp holders may require the larger size wire.
If you examine ZIP CORD closely you will note that while both wires are molded into a common insulation, one conductor has a smooth covering and the other one has very small ridges running the full lengh of the wire. (You may need to feel the wire with a fingernail to locate the ridges.) The wire with the ridges is technically called the "Identified Conductor". Some Zip cord also has a color coding on the wire. In this case the smooth side will be copper wire and the ribbed side will have a silver colored wire.
When wiring a lamp or appliance with Zip Cord the "Identified Conductor" is supposed to be connected to the circuit common (Nuetral or white terminal) and the smooth conductor is to be used as the powered conductor.
Most switches & lampholdeers are also color coded with a Copper screw for the powered conductor and a silver screw for the neutral. In this case the ribbed "identified conductor" should be attached to the silver screw.
In your normal house wiring the cables have a black wire for the powered conductor and a white wire for common or neutral. Think of the silver screw as being a white metal when compared to copper. You then simply connect copper to copper and white to white.
In reality a lamp will work just as well if the wires are reversed, however, if the wires are reversed the outside shell of the lampholder is now the powered conductor and it could present a shock hazard if someone were to touch it while touching another grounded surfacee so for safety sake, it is important that a lamp be wired correctly.
For safety reasons a switch should also always be installed on the powered conductor.
If you will examine the attached drawing I prepared you will see that the self wiring switch has two Vee shaped cutters that the end of the wire rests in. When to cover of the switch is put in place it has two molded extensions that press the wire into the vee notches. As the wire is pressed into the notches the cutters cut through the insulation and make contact with the wire inside the insulation.
There are some common conditions that may result in the problem you are having:
1. One of the wires may have slipped out of the Vee notch while you where attaching the cover and it did not make contact.
2. Your lamp may have a heavier guage of wire than what your switch is rated for and the cutters are not large enough to sufficiently penetrate the thicher insulation on the heavier guage wire.
3. One of the wires may have slipped out of the molded wire channel inside the switch and is between the two halves of the switch body preventing the switch body from closing suffiently to make contact.
