There should be continuity on the pressure switch connector between the brown/black wire (from the pump relay) and the brown wire (earth) when the accumulator pressure drops below 140 bar, turning on the pump relay and thus the pump. Obviously if the pins are corroded and no contact is made, the pump doesn't run.

Now you just need to look at the ABS warning light.........let us know if you need help or if it has simply been disconnected.