I have two MIM jazz basses. As an experiment I copper foil shielded the pickguard and cavitys and changed the wiring to a single point ground at the output jack of one of them I even went as far as to installa brass tube in the wireway from the bridge pickup to the control cavity soldered to the foil in both cavitys I also removed the string ground. The shielded bass hummed less but still hummed. I used a compass add found that the pickups are magneticly the same and wired the same. The glue that holds the magnets to the steel poles looks to be like a contact or hotmelt type. I placed the neck in my wax potting setup and let it heat up for an hour at 150 F I removed the pickup and the magnets pulled off easly I then flip them around white side out and they seemed to glue themselfs back on BE VERY CAREFULL THE PICKUP ARE VERY HOT.

I installed them back in the bass and flipped the wires I dropped the neck pickup way down. It is now very quiet when volumes are adjusted. There also "SEEMS" to be something about the 20% beeswax 80% paraffin wax mix that warms up the sound. 

 Vol. Taper
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Stick a 500k-1meg trimpot between the wiper and each side lug - with alligator clip leads - and play with them until you're happy. RG's and Jack's articles should provide all the guidance you need.