Hi
Simple Märklin fan from a long time here but without direct connections with Märklin.

Why four positions?
This allows to have one position being stopped at station with headlights on.
This further allows to have 2 locos on the same circuit with one being active while the other one is stopped (at station).
Agreed this last operation may require some resynchronizing using the manual lever to change the relay (in use by Märklin until approx. 1960.
According to some authors, the "other" reason for Märklin not to use the ratchet relay (2 positions) before 1959 was patents.

So the four-position relay uses a drum being rotated by a solenoid by 1/8th of a turn with 2 contacts
Here is one late version with an anti-kick contact

Fig 1 : the magnetic circuit
Fig 2: the solenoid and contact holder
Fig 3 : the drum Notice the 2 adjacent rotating surfaces 1 is metal and the other is bakelite
Fig 4 : the drum axle holder
Fig 5 : the ratchet
Fig 6 : the anti-kick contact. It is a later addition (around 1958). When the armature is closed, the nut on the ratchet disconnects the motor to prevent the "Bocksprung" (buck jump)

The spring is not represented

Cheers
Jean

Thank's Tom! Because my layout is a horse shoe dogbone, the direction depends on where I set the train on it, as well as the direction. Trains in unison follow each other so as not to collide. Once I turn headlights on, I know which way it will run, then I check the train parked in the station before I set them off to go. The station is on an oval, and the town oval on the opposite side has one, so turnouts also have to be set so trains don't enter them or exit them when two or three are running the entire loop. I don't use automation or events much because there are not enough signals nor blocks.