TAILGATE WINDOW TOYOTA HILUX

MY WINDOW GOES UP BUT WILL NOT COME DOWN I HAVE TO TAKE THE COVER OF THE MOTOR AND WIND IT DOWN WITH A SPANNER.I HAVE TESTED THE MOTOR WITH CABLES FROM THE BATTRY AND THE WINDOW WILL GO UP AND DOWN BY REVERSING THE CABLES.I EVEN BYPASSED THE SAFETY SWITCH WITH WIRE BUT STILL NO JOY.WHEN I USE THE SWITCHES I GET A CLICKING NOISE FROM THE UNIT ON THE LEFT HAND SIDE.HOW CAN I FIX THIS PROBLEM ITS DRIVING ME INSAIN PLEASE CAN YOU HELP ME ON THIS ONE TAAA