I just had to rebuild my tone circuit, so I bought the parts from Elderly Instruments
. While I was there, I spoke with the tech, and he pointed out to me that most of the wiring diagrams for Fender basses on the 'net are actually incorrect, specifically including all the Seymour Duncan diagrams. While these diagrams will give you a working circuit, they are not completely right, and won't allow the circuit to work as intended by Leo. These circuits will overly boost the bass when the tone is rolled off.
For a tighter, more controlled bass, use the correct diagram. The correct diagram can be found at Fender Support
The main difference is in the wiring of the capacitor, so take note of that. Also, be sure to use the correct wires, as heavier wires will give a noticeably brighter tone. Of course, if that's what you want, then use heavier wires. This can be augmented by using 500k pots rather than 250k.
So, I guess what I learned is that the commercial isn't correct: it turns out that they can, indeed, put something on the internet that isn't true.