I had a TBird pro with a great hum noise issue. After I've read this forums (and others) I came up with, what I think is the correct solution. Here I share with you
1) The wiring schematics in the page are correct
2) I don't think the preamp is the SD BEQ-2, just another two band preamp. I remember searching for it with the part number and finding it ,,,but not at SD
3) I don't think that changing the volume pot for 250K would yield aa 3dB volume gain (much less a 6dB gain with 512K). If you look closely at the schematic, you see you get the signal straight from the preamp output pin when the volume is maxed. Howeve rthere might be a small increase in volume depending on the amplifier input impedance
4) The pickups are PASSIVE with an active preamp (as this is the most common configuration on active basses). There's no such thing as ACTIVE/PASSIVE pickups. EVERY BASS (and guitar for that matter) than can work both as active/passive, is a passive pickup/active preamp combination, changing to passive simply bypasses the preamp. One of the the wiring diagrams in this thread confirms this. The RED WIRE in the pickup is for coil splitting, you can definitely check this with a multimeter, it's NOT FOR POWERING THE PICKUP. However, as the noise is picked by the pickup coils, running a current through them might mitigate the problem.
5) The correct approach is to properly shield the pickup cavities with copper foil, o painting it with conductive painting. (in my case the preamp cavity was painted with conductive paint, but you could check yours)
6) Note that it also has to be properly grounded, all pots bodies bust be grounded, and if you use copper foil or paint with conductive painting, this is already done
Hope this is useful
Antonio
