Tried wiring my Dual Humbucking Warmoth Strat with 50s wiring

[Schneidas]

So I have this Swamp-Ash Strat Warmoth Body with H-H, so just dual humbuckers with no Single in the middle and a 3-way selector switch.
I figured giving 50s wiring a try, so got the attached wiring diagram and followed everything.

Now all seems to be working fine except the middle position on the 3-way selector switch: there is no sound at all, while I should get Neck and Bridge humbuckers combined.
Any idea what I need to change?

 

[stratamania]

Your switch has nothing connected in terms of pickup signal when in the middle position.

The diagram also says gorunded rather than grounded.

Look for a Tele wiring diagram to see how the 3 way needs to be wired.

 

[Schneidas]

Ok, so after looking at a Tele wiring diagram, I'm still stuck.
I don't understand how a switch works exctly and don't have any idea how a closed circuit works.

So in simple terms, what would I need to wire in for the middle position to get active, while keeping the 50s wiring?