software

I just put a tapped SSL6 in a guitar. I intended to use a no-load pot to 'spin' the tap; wire the full-coil lead to the selector and connect the tapped lead to the wiper of the no-load pot. By grounding the 'bottom' terminal, at '10' the tapped lead is isolated, and rolling down to '0' gradually grounds the tapped lead - thereby grounding out half of the coil.

It works, but with the pot on '0' the tone is not the same as if the tapped lead was made hot and the full-coil lead isolated; the tone is dull, as if the pickup is being loaded down. At first I thought this might be because I was using the portion of the coil furthest from the magnets, so I moved the pot from ground to hot (shouldn't make a difference), but this resulted in the same thing.

Electrically this makes no sense; it should work. Why doesn't it?