Graph Tech Ghost Passive Volume Kit for Guitar or Bass
The Passive Volume Kit lets you connect ghost saddle pickups directly to your 1/4" output jack. The sound of the pickups is rather harsh on its own, so it will not sound like an acoustic guitar without further signal processing outside the guitar.
Click here for the wiring diagram
For Acoustic sound directly from your electric guitar, you need the Acousti-Phonic Preamp.
The Passive Kit includes a high-impedance volume pot and other components that help impedance-match your acoustic pickups to your amp, to prevent loss of high frequencies (muffled sound).
The capacitor is used to prevent the loss of higher frequencies as a pot is turned down, it is sometimes accompanied by a series or parallel resistor, to limit the amount of treble being retained and to match it to the pot's taper. They are not necessary in every install.