I'd say step one is use a cordless drill to try to drive the glass up and down. Chuck the drill onto the cable, I believe reverse is up, and forward is down.
If it goes up and down somewhat easy the power motor is probably too weak.
If it is sticky, or sounds strained going up or down you'll have to disassemble it further to find out why and rectify the problems as you find them.
Step one is get the glass as far down as it'll go and open the tailgate. At the top corners, remove the hard black rubber coner pieces...should be two screws each.
Remove the inside and outside wipers. Using a flat blade screwdriver get the tip between the wiper and the gate and twist the hnadle a bit. This will open up the clip and allow you to get the clip out of the slot. Do that for all the clips starting at one side and working across.
Remove the access panel (it sounds like you already have) and using a drill raise the glass up a few inches. At the base of the glass you'll see a steel track the glass is attached to. There are two tabs on that steel track and each one has two small bolts. Remove those bolts and carefully pull the glass out of the gate.
With the glass out, work the regulator up and down using the drill again. Everything smooth, move on. Not so smooth...use some brake Kleen to remove the gunky sticky grease, and re-lube. Try the regulator up and down again.
Remove the channel tracks from the ends of the regulator arms. Check the nylon rollers at the tips of the regulator arms. They should be round and turn/roll freely. Check the channel track...is it full of scaly rust and mud and junk? Clean it so it's smooth again.
Grab a flashlight and look at the side tracks for the glass. These are often rusted out, felt missing. If they're still in one piece and have at least some felt left you're good there.
Check the bottom of the tailgate now. You may want to remove the regulator for better access, it's only 4 small bolts, you have to postion the arms specifically to get them all.
The bottom of the tailgate often fills with crud...you'll want to clean and dry that. With the regulator out of the way, try the glass in the side tracks and see if it will go up and down without hanging up anywhere. Clean and lube the backside of the regulator.
With the regulator out you'll have access to the key switch stuff. The key should turn a similar amount to the door locks, close to 90 degrees.
Re-assembly is pretty self explanatory. The wipers at the top...I just tighten the little tabs and work them back into place.
Rene
