Lead-Acid Battery charger using LM350 and LM301
the LM301 datasheet shows and Sziklai pair Q12,Q11 pulling down on the output via R10 and R11, it is these components that pass the bulk of the LED current when the output is low. 


the PNP transistor is controlled via the pair of 4.7K resistors by the op-amp that is cating at a comparitor, the trasistor is either off or fully conducting 

the 1.5K will pass about 10mA when 12V is selected or 5mA when 6V is selected , that will add about 1V or 0.5V to the voltage on the 100 ohm resistor, which itself lifts the whole LM315 regulator. (these figures are all estimations they are inaccurate but should be in the right ballpark.)