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Jon, you ask----"the "Light Switch" has a terminal marked "resistor terminal" with a green-on-yellow" wire connected to it which appears to be the same green-on-yellow wire that emerges from the harness at the generator "Field" terminal. Does the "Light Switch" have a built-in resistor to limit the field current to the generator?"-----Yes, the light switch has a resistor to limit field current when the lights are turned off [early styled tractors]....With the lights on that field wire is grounded at the light switch to give you a full field. The generator should also have an adjustable 3rd brush to fine tune the generator output for conditions of use.. ~"there doesn't appear to be a master switch to disconnect power from everything. Does the "Light Switch" also disconnect the power to the generator field or is it only an insulated mounting for the resistor? I don't think they would only have the generator charging the battery when the lights are turned on"-----No, the light switch doesn't disconnect power TO the field. The field is powered from within the generator by the 3rd brush [or {A} post on the later systems]. All the light switch does is either ground the field [full field, lights on], or ground the field through the light switch resistor [partial field, lights off]. The generator is disconnected from the battery & tractor wiring by the cut-out relay [mounted on the generator]...There is a set of magnetic controlled points in the cut-out relay that monitor the generator's output voltage & when the generator output is higher than the battery voltage the cut-out closes & allows the generator to charge the battery. When the generator output drops below battery voltage the cut-out opens & disconnects the generator's armature [output] from the battery & tractor... The generator CAN charge the battery with the lights on but there isn't much left after the lights get their share of the operating current supply. [simple as that].... ~On the later D's [after about mid 1949] the light switch isn't used for generator field control & the charging system uses a conventional voltage/current regulator instead of a cut-out relay. To tell the difference....A cut-out relay has a rectangular cover & only 2 terminals,,,A voltage regulator has a square cover & either 3 or 4 terminals, or could have 3 terminals & a 4th wire that goes to the generator's [A] post...
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