Illustrations from the MTSC linked earlier.
If the points are stuck in the upper position, current flows through with no resistance.
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When the voltage is above the set point (lets call it 14.5 V) the regulator's electromagnetic is strong enough to pull the points to the low position. Current flows the parallel resistors and then takes the easiest path to ground.
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If connection to ground is a fusible link. If its broken then current will flow through the rotor windings instead.
Same flow path as when the points are in the middle position.
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So make sure the link from the lower point contact to the ground is good.