More like "a specially moulded connector to have all the terminals located" - the field coil isn't polarised, so it doesn't really care which way it's hooked up (nor does field coil polarisation have anything to do with output polarity. Alternators generate AC voltage natively, whichis converted to positive DC voltage by the rectifier assembly. You'd have to reverse all of the diodes in the rectifier to generate negative DC voltage instead...)
It's just something that's there to make life easier for Zimbu the Monkey - just like the moulded rubber bit that locates the wiring on later model starter motors (if you can't tell the difference between the solenoid trigger lead and the starter motor power lead, you shouldn't be anywhere near a wrench alone!)
