TAIL GATE LIFTERS FAILED TO COMPLETELY LIFT THE TAIL GATE. NOT NOTICING THE TAIL GATE WAS SLIGHTLY LOWER THAN NORMAL, THE DRIVER, WHILE STANDING ON THE GROUND TO REMOVE GROCERIES FROM THE BACK, LEANED INTO BACK OF VEHICLE AND STRUCK THE TOP OF HER HEAD ON THE TAIL GATE, SUSTAINING A CONCUSSION. SYMPTOMS INCLUDED NAUSEA, HEADACHES AND DIFFICULTY CONCENTRATING, LEAVING HER UNABLE TO COMPLETE HER NORMAL TASKS FOR THE DAY. THE SYMPTOMS LASTED 2 DAYS. DRIVER'S HUSBAND CAME OUT AND IMMEDIATELY CONFIRMED THAT TAILGATE HAD FAILED TO OPEN COMPLETELY AND HE DETERMINED IT WAS NO LONGER OPENING COMPLETELY, REPRESENTING A PARTIAL BUT DANGEROUS FAILURE OF THE LIFTING MECHANISM. THE TIME WAS APPROXIMATELY 4 PM; THE TEMPERATURE WAS APPROXIMATELY 48 DEGREES. WHAT MAKES IT PARTICULARLY DANGEROUS AND PERNICIOUS IS THAT THE MECHANISM THAT USED TO OPEN THE TAIL GATE ALL THE WAY UP, PROVIDING AMPLE HEAD CLEARANCE, WAS NOW LEAVING THE TAIL GATE OPEN BUT WITH REDUCED HEADROOM. THE MECHANISM THAT USED TO PROVIDE SUFFICIENT HEAD CLEARANCE SO ONE COULD STAND BEHIND THE VEHICLE AND LEAN INTO THE REAR WAS NOW ONLY PARTIALLY OPENING THE TAIL GATE, TO A POINT LOW ENOUGH TO CAUSE A CONCUSSION BUT NOT LOW ENOUGH TO BE NOTICEABLE. THE CHANGE FROM HAVING AMPLE HEADROOM TO NOT HAVING ENOUGH HEADROOM CREATED A TRAP. *TR