If possible, try a unit that is known to work with the suspect wiring to determine whether the problem is your unit or the wiring. Be sure the calibration number and stroke mode are set the same as your unit.
Check the wiring for visible cuts or nicks.
Check that both sensors are correctly aligned (i.e. the black sensor aligned properly with the magnet and the blue sensor aligned properly with the impeller).
Check the impeller for debris and make sure it is not damaged.
Check that the metal contacts on the unit depress easily and rebound level to the back surface of the unit.
Check the metal contacts on the mounting dock and make sure they are flush with the surface of the dock.
Clean the contacts on both the control unit and the docking station with Bon Ami (a non-abrasive cleanser available at most local stores).