[Jeff Goldman]

Can a bad brake accumulator prevent ABS pump from operating? Or is this more likely due to a bad ABS pressure switch? Relay checks out OK (relay test becnh test OK, and I have 12v at the control pin). Pump operates if I jump it at the relay pins. Can a collapsed accumulator force the pressure switch to never trigger?

 

[Bolt]

Short answer: NO

Longer answer:Yes, the switch being faulty would be a possible cause.
Check for continuity on the switch. it should ring out as closed with no pressure.