To function correctly, the battery pack, the servomotor and the CBL,
CBL2 or LabPro must all have a common reference point, or "ground."
Cut the black (negative) wire from the battery pack roughly even with
the end of the blue wire. Remove about 5 mm of insulation from each side
of the cut black wire.
Use a screwdriver to loosen the black wire terminal in the phone jack,
insert the bare section of the two black leads under the washer, and
retighten. The battery's negative can now be connected to the CBL's ground
through the phone wire, and to the motor's ground through the other connector.
