I have a nearly 40 year old Cortez jazz bass that I'm changing the pots on. I noticed it has three wires per pickup; one red going to the center lug on the volume pot; one white and one blue, both going to the ground on the top of the pot. All the jazz bass pickups I have worked with in the past have only had two wires. What is the purpose of the third wire? Does this third wire allow for any special wiring options?