never done one on a mustang, but they are a PITA on Acuras. i have to use an impact driver about half the time to get off the screws on the end. the actuator should be located on the end of the door, the part facing out when the door is open. the whole install is by feel, since you cant see inside the door to line everything up. you may or may not have to remove the regulator and window track for clearance. when you finish up, make sure all the steel rods are connected back where they were. it sucks to put everything back together only to find you have to take it back apart b/c you the door knob isnt attatched to the rod