The piezo element is used on the electric guitar to convert the vibrations from the guitar string into electricity. In order to install the piezo element, or "pickup" as it is also called, the plastic casing on the pickup was cut away, and a rubber foot was attached onto the center of the element. A hole was then drilled in one of the PVC pipe caps, and the plug was cut off of the audio extender cable, which was then fed through the hole in the cap. Next, a cable tie was fed through the non-notched hole out the bottom of the pipe. The cut end of the extender cable was then taped to the cable tie and pulled through the non-notched hole.
Piezo element's 2 wires: ground (black) and signal (red)
Extender cable's 3 wires: ground (bare copper), left and right (both insulated)
The website provided a useful tactic to determine which wires were which. When the extender cable is plugged into a set of speakers, the left speaker makes a buzzing noise when the Left wire is held, and right speaker makes a noise when the Right wire is held. When the ground wire is held, so noise is made. The piezo ground wire was soldered to the extender cable ground wire, and the L and R channels were soldered together to the piezo signal wire.