Old Washburn WB-6 Bass

[1bw]

I've been working on an old Washburn WB-6, 6-string bass
in my spare time. I can't find an electric schematic anywhere?
The bridge pickup is a washburn #663 but the neck pickup the number is worn away! (They are Jazz Style pickups, 3 11/16" X 0.73)
I've refinished it, worked on the neck, and now I'm trying to quiet it down, (60 cycle hum).
It has 1 volume, bass boost, treble boost, and a 3-way switch.
Currently when I have the switch in the middle position it's quiet, when I move the switch to neck position or bridge position it has major hum. I believe it's a grounding issue.
Any thoughts out there?
Thanks,
1bw