Dunno what you did, but you did something wrong. You already figured that out.
- Make sure your switch is the same kind of switch
- Make sure that you're wiring to the correct lugs (obvious)
- Make sure that if they're the same make of pickup, that you use wires following the same colour codes. So, if Stewmac's diagram has a white and black wire, but yours has white and red, just make sure that you're consistent with how you "translate" the colours.
The wiring might seem discrepant, but remember that when the switch is all the way back, because it's a lever, it will create a circuit on the lugs that are forward. But it doesn't matter-- if you do it backwards, just flip the switch around. ;-)
Yes, the middle position should be both pickups on.
Greg