Think I figured it out. A friend has the Bart 2-band in his bass and brought it over for comparison. Unlike the diagrams on the Bart website, the colored wires actually matched up.
White goes to the trim pot, green goes to the third lug on the volume, black to the input jack.
Found this in a previous thread for P/humbucker/reverse P wiring:
P switch (DPTT on-off-on):
1 2 3
6 5 4
1 wh/shield ground
2 blue
3-6 green/orange
5 red
4 black hot
Explains the green wire between 3 and 6 on my unit.
I know there has to be a bazillion different ways to wire the pickup up...anybody have some alternative ideas? I'm not tackling this job until the weekend when I have the time and ambition to experiment.