540PTC wiring diagram

Does anyone have acess to the above or have one that can tell me what the controls are suppose to actually do? I just bought a used one, and it's obvious it's been messed with inside.

For those of you that don't know, here's the layout:
single coil and humbucker in the bridge position, one volume, one on/off mini toggle switch (coil tap), and one 3 way mini toggle (on/off/on) switch for selection. My problem is that the middle position on the 3 way does nothing unless the volume on an amp is way up. I have replaced all the switches, pots, ect. and the pickups test ok. I know I am missing something obvious, but I can't seem to find it. Is it suppose to be an on/on/on switch? Any help would be appreciated!
Thanks,
Josh