If you do that, I’m pretty sure it flips the phase of the pickup. I’ve installed phase switches before, and when you are using one pickup alone, they don’t change the tone in my experience (though I don’t know if that is electronically accurate), BUT if you only do this for one pickup on a two pickup guitar, it will massively change the tone of the setting with both pickups on (unless you wire both pickups like this then they will be in phase again).
