What if I am installing the ghost system into an instrument that does not have any magnetic pickups?Updated 7 days ago

If you have an instrument with a metal bridge plate, it would be good practice to ground that plate rather than leave it floating because the bridge is a big chunk of metal near the pickups and their wires, which are high-impedance and thus prone to pickup. If the bridge is floating, it will tend to help to couple the ambient 60Hz field with the pickups and wires. On the other hand, if it is grounded, it will tend to act as a screen, shielding the pickups and their wires from the ambient 60Hz field.