For me, the most difficult part of going into the door has been removing the door handle and window winder handles. If you've never removed a door panel before, this will be the hardest part of the job. Be patient. Easier on the later style with the 'omega' clips. On my 444 there are hardened pins. You have to apply a fair amount of pressure on the escutcheon/panel and spring in order to access the clip, and then pop the clip off the shaft on the mechanism affixed to the door. As Phil says, once you've got it apart, it's all apparent. Be careful not to cut yourself on all of the sheet metal edges your wrists and arms will come in contact with - a fair amount of arm gymnastics required working inside the door. WD40 the tensioning mechanism to loosen up the nut.
Either the cable has come off the pulley wheel or as Ron suggested, the ferrule has become unsoldered. I've seen one case where, over time the nut on the tensioning spring/bolt has worked it's way loose.

Patience.

Also, when replacing the grab handle, be careful not to over tighten the two screws too much, or you'll just pull the metal inserts in the foam through the handle and your handle will be forever loose.

When removing the panel/clips from the perimeter which hold the panel to the door, I use a putty knife or a brake adjusting tool, and BE SURE TO PRY BETWEEN THE CLIP AND THE DOOR., not the panel and the door. Panels are old, dried out and are fairly easily broken, especially along the bottom where wet/dry/wet/dry has compromised the little integrity the fiberboard panel ever had - the clips rust and the and unless you pry the clip, the clip will remain and the panel will bust.