The components you install should include earthing/ground connections when installed as intended.

Adding another earth/ground lead may actually increase the likelihood of hum in your system, since it can produce "ground loops" due to the difference in voltage drop on competing earthing leads, which causes current flow from one "ground" to another "ground."

Exsmine your final wiring and be sure that good, well connected leads, provide a single path from each component part to the circuit ground on your amp/pickup, and you should have a properly configured installation.

John