Wiring Stepper Motors in Series
If you want to run 4 Z (or Y) motors with RAMPS, it is possible. To do this, you must have a 24V system (so each series motor gets 12V). This allows you to stay within the current limits of the drivers, without having to use larger drivers if you were running all 4 in parallel.
Picture Makes Sense
Picture Does not Match Diagram
From . Note the wiring picture above does not match the schematic in the link.
Wire as in picture. That should work.