Some advice on this prewired Jazz bass wiring harness.

When you turn down a passive volume control it “dulls” the sound a bit due to the resistance (in fact, if you look up some of @RobbieK stuff he shows that most of what a passive tone control does is because of the added resistance. The cap comes into play mostly at the end). The treble bleed is a small value capacitor across the hot and out of the volume pot so it keeps some of the high end in the signal as the volume control(s) are turned down.