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The power assist in the H3 comes from the motor that pressurizes an accumulator to supply brake system boost, versus a vacuum cylinder as used on most other vehicles. This pump will cycle on an off to charge the accumulator whenever required, not just during ABS operation. (The accumulator is the round cylindrical item to the left of the brake master cylinder.)
During ABS operation, it will also run, as well as you will hear the clicking of the solenoids inside the BPMV cycling pressure to the wheels cylinders, as required.