How do I set the PU height?

I just replaced the PU selector switch and now I can't get the PU height back in place. I have the action set pretty low but not extreme. I started with the PU's as low as they can go and I heard a buzz in the low E when struck open.
I raise it up a little and the G hits the PU in the upper octave. It was perfect before I replaced the switch so I know it can be done. What do I have to do?

I should mention that the problem is mostly with the neck PU. When I have it set low enough for the strings to clear there is a slight buzz sound.