Hello,
English is not my native language and I'm busy as hell but let's try.
According to your schematic, the widest tabs on your slider are the "common" lugs (I've colored these parts in pink in my schematics below). Position 1 = tab 1 connected to common, position 2 = tab 2 connected to common, position 3 = tab 3 connected to common (dumb sum up but at least it should be clear).
I assume the pickup(s) used to be Duncan(s).
On these basis, below is how your slider(s) might be CURRENTLY wired - or at least how I'd wire the whole to obtain a north / series / south arrangment...
In this FIRST schematic:
-black wire goes to hot, green wire goes to ground (with the bare wire).
-the tabs number "two" are connected to nothing.
-Position 1 puts white and red to ground, so the north coil is between ground and hot (and is therefore enabled), while the south coil is shorted (being connected from ground to ground).
-Position 2 just leaves white and red together on the common lug, connected to nothing. So the coils are in series.
-Position 3 connects white and red to hot, so the north coil is shorted (being connected from hot to hot), while the south coil goes from ground to hot and is therefore enabled.
View attachment 101174
Now Below is an attempt to fulfil your request.
In this SECOND image...
-The two rows of tabs are used.
-On the upper row, the white wire is connected to the common lug in pink.
-On the lower row, the red wire is also connected to the common lug in pink, but white and red wires are now separate, each having its own common lug.
-Black wire still goes to hot, green wire remains connected to ground (with the bare wire).
-Position 1 connects white to ground while the other end of north coil goes to hot. North coil enabled. South coil has its green wire to ground and its red wire to ground also. It's shorted.
-Position 2 connects black to ground and red to hot. Both coils are enabled in parallel (white to ground and black to hot // green to ground and red to hot).
-Position 3 connects red and white to hot: south coil is enabled (going from ground to hot) while north coil is disabled (going from hot to hot).
NOTE: I could have left the white wire connected to nothing in position 3 (IOW: tab 3 of the upper row connected to nothing) : the choice is up to you and depends on possible parasitic noises noticed with one wiring or the other.
View attachment 101175
Our local specialists will correct my attempt if I'm wrong. I can't do better for the moment, life is calling me.
Good luck in your wiring work...