I have been following this Seymour Duncan diagram, and either I am missing something or there's an error somewhere on the diagram.

The controls don't do what they're supposed to do. Electronics are not my strong point. Perhaps someone can spot my wiring error in this photo:

Pots from left: Volume, tone, mixer
Volume:
The top terminal has one black (ground) wire from the jack and another black wire soldered to the casing.
The middle terminal has the white (hot) wire from the jack.
The bottom terminal has one end of the tone cap and the white (hot) wire from the lead pickup.
Tone:
The top terminal is unused.
The middle terminal has the other end of the tone cap.
The bottom terminal has a black (ground) wire soldered to the casing.
Mixer:
The top terminal is unused.
The middle terminal has the black (ground) wire from the lead pickup and the yellow (hot) wire from the rhythm pickup.
The bottom terminal has the black (ground) wire from the rhythm pickup and another black wire soldered to the casing.
1/4" jack (not shown):
Hot side -- white (hot) wire to middle terminal of volume control.
Ground -- black (ground) wires to top terminal of volume control and to bottom of bridge.