What was found
PILOT EXPERIENCED FAILURE OF ALL DISPLAYS IN AIRCRAFT. AUTOPILOT AND RADIOS APPEARED TO BE OPERATING, BUT NO DISPLAY AVAILABLE. COULD NOT DUPLICATE ON GROUND. CHECKED WIRING AND DIMMING UNIT. FOUND EVIDENCE OF ARCING ON RING TERMINAL AT LOAD CONNECTION. REPLACED DIMMER UNIT AND RING TERMINAL ON WIRE. OPS CHECK GOOD. IT APPEARS THAT RING TERMINAL BECAME LOOSE. THERE WAS NO PLAIN WASHER INSTALLED UNDER THE LOCK WASHER ON SCREW.