The field windings are supplied power from the battery via the ignition switch and regulator.
When the armature and the field windings are connected in series, the whole motor is referred to as "series-wound".
Tustin, who did most of the design work, found that the system had a large time constant, due to the inductance of the field windings.
The DC motor is made in two parts; the rotating armature and the fixed field windings.
The field windings, also called the stator, surrounds the armature.
The field windings are made of tightly wound coils of wire inside the motor case.
The armature is connected to the field windings through brushes.
A series-wound motor has the armature and the field windings connected in series.
These motors are broadly the design of the brushed DC motor with series-connected field windings.
Your field windings are full of vines, I'm afraid.