#3 seems to be the evil california 3-way we originally talked about. Hot and neutral go to the traveler terminals and the commons go to the light.
Andy, I know it under the names Hamburger Wechselschaltung, Sparwechselschaltung or Kreuz-und-Gewitter-Schaltung.
One additional problem is when an old, worn-out switch arcs you have a nice fat short and don't know why.
In Germany that system was once used to feed a grounded receptacle and 3-way switch with only 2w+ground cable. How? Black = hot. grey = Neutral with jumper wire to ground screw at receptacle (once legal) and red wire (actually intended to be the ground wie, but that wasn't ever that strict, according to code red could also be used as a phase) was the fixture wire.
Simple and ugly, and probably outlawed in the 1920ies or 30ies. "Classic grounding" was allowed until 1973.
