It is generally accepted that the best way to ground electric guitar wiring to prevent interference and ground loops is to connect a common ground wire to the biggest hunk of metal on the guitar, that being the bridge. A semi-hollow, or chambered, body is somewhat less common than the usual solid or hollow body guitar, but the technique for connecting the ground wire to the bridge remains the same.
Remove the strings, bridge, bridge studs sleeves and rear control cavity cover from the guitar's body.
Drill a 1/8-inch hole from the bridge stud sleeve hole closest to the control cavity in the direction of the cavity. You will need to start the 1/8-inch hole from near the top of the stud sleeve hole since the drill bit does not bend, and drill as shallow a downward angle as possible to avoid drilling though the bottom of the body. The control cavity is large enough that by just drilling in that general direction, the hole should end up coming through in the control cavity. Vacuum or shake out any small particles of wood that fall into the control cavity.
Strip 1/4-inch insulation from both ends of the guitar circuit wire.
Thread the wire though the hole that you drilled in Step 2 so that only one stripped end of the wire is visible in the bridge stud sleeve hole. Fan the strands out some so that they lie relatively flat against the wall of the bridge sleeve hole.
Insert the bridge stud sleeves back into the holes. The sleeve closest to the control cavity will not easily slide back in since the end of the wire now occupies a portion of the hole. Tap the top of the stud with a wooden or rubber mallet until it seats properly. The tight fit holds the wire against the metal of the bridge so that no soldering or adhesive is necessary.
Solder the other end of the wire to the bottom of the casing of the volume pot where the other ground connections from the controls are located. To solder a connection, hold the exposed core of the wire against the connection point. With the same hand, hold a 4- to 6-inch section of rosin core solder directly above the connection. Hold the tip of the heated soldering iron against the end of the section of solder until it begins to melt. As the solder begins to flow onto the connection, remove the soldering iron from the connection and allow it to cool.
Replace the control cavity cover, reinstall the bridge and string the guitar.
Always unplug the guitar from the amplifier before performing any service on the instrument.