I found this searching around the net and thought I'd share it with you guys like me who want a 500K volume pot for the humbucker and a 250K volume pot for the single coils and didn't have a clue how to do it. Of course the color of wires to be used would have to be converted from the Seymour Duncan color scheme to the BKP color scheme.
Using a 500K volume pot or 500K volume and tone pots, you can get 250K out of it when switched to the single-coil(s) by putting a 500K resistor in parallel with the volume pot. The way to do this is to solder one end of the resistor to the same lug on the switch where the single-coil hot wire connects. The other end of the resistor gets soldered to ground.
When two resistors of the same value are in parallel with each other, the total value is divided in half. So, we have 2 resistors, 500K each (the volume pot is a variable resistor, folks). 500K / 2 = 250K.
The actual formula is:
R1 X R2 divided by the sum of R1 + R2
In this case:
R1 = 500K
R2 = 500K
Using the full numerical values:
(500,000 X 500,000) / (500,000 + 500,000)
250,000,000,000 / 1,000,000 = 250,000 (or 250K)
Since I didn't have any 500K resistors laying around, I used 470K instead. This gets me about 242K when the switch is in the neck position AND middle position. But when I switch to the bridge humbucker, it's the full 500K.
If you don't have or cannot find any 500K resistors, use either 470K like I did, or better yet, put two 1Meg resistors in parallel to make 500K. Just twist the leads together and solder them in place.
The diagrams:
There's a diagram for H-S using a 3-way toggle and one for H-S-S using a 5-way lever.
