I finally managed to get the 15 pin plug off the ABS board module, and the module unscrewed and removed from the ABS pump assembly.

The lower two pins on the 15 pin connector on the ABS board module meter out to the relevant two pins on the top of the board with zero resistance and the contact is not lost as the module is shaken or moved, so I think the fault lies elsewhere.

When the engine is running, there is ca. 14V on the fuse for the ABS pump, but only 9V on the hot wire of the ABS module plug, so maybe that isn't enough to run the ABS pump, and I am now off to try and find out where this voltage loss is occurring