i want to add to Louisa Metler's answer following or what its worth.

i would connect the pups/pots setup to the GND on the volume pot with 1 wire to the GND jackinput.
all  the other GND wires direct to that same GND jack connection.
you can bundle them dough
but u get two wires to that jack GND.
1 from the 'sound' system
2 from the GND system like cavity's, switch etc.

not that i can explain it with some theory ore something, but that is what i would do.