In most cases you may find:
1. A winding for regulation similar to an alternator. Current induced here changes the voltage.
2. A winding that is designed to produce a very small amount of DC with #1 turned off.
The #2 is the "kick" for #1. There has to be residual magnetism to get the control circuit up an running.
3. The oil sendor switch, No oil, no output.
4. Frequency is changed by the RPM. Not in range - no output.
5. Output windings, 120, 240, 12 V
Usually the control winding needs to be kicked with a 12 V supply in the right direction, so it's a quick connect to +12 at high current that magnetizes the field.