Ray Drouillard's 
Wagoneer/Cherokee Tailgate how-to
When I put down the glass and pulled the inside handle, nothing happened.
 The first thing I did was to remove the twelve screws that hold on the
carpet.  I removed the carpet from the tailgate, then the access panel
(12 screws).  I removed the screws that hold on the lever assembly in the
middle of the tailgate.  I put the window back up and got into the back
of the Jeep by first lowering the back seat.

The next step is to trace along one of the two bars that go from the
handle in the middle to the latches.

In normal operation, pulling the handle up pushes on the passenger side
bar and pulls on the driver side bar.

There are two screws that hold a swivl mechanism at the end of the rods. 
Remove those screws (two per side).

If you reach around by the latches, you'll find a small lever that will
release the latch on the tailgate.  If you lift both of them and go
outside and lower the window, you'll find that the tailgate is loose. 
The latch is on the inner step.  It needs to be pulled again to release
the door all the way.

Unfortunately, you can't reach in there with the glass down.

Go inside the Jeep with two halves of a coat hanger,  Bend a real short
"U" in the end of each one.  You can't push it between the glass and the
seal, but you can push it onto the space right at the edge of the glass.

Thread it down through and use your other hand to hook the little hook
onto the lever.  Bend the top of the hanger down to hold it into place. 
Do the same for the other side.

Go outside and carefully lower the window.  Grab the two pieces of coat
hanger and pull.  Viola!  The door is down.

From there, you might want to lubricate the mechanisms.  You'll be doing
good to not get any on the glass, however.

There is a safety lever on the passenger side of the tailgate right next
to the latch.  If you hold that while operating the key, you can put the
window up.  Be VERY careful.  Only put it up enough to get it out of the
way.  If you put it too far up, it'll bread off and fall to the concrete.
 Very expensive.

If the mechanisms aren't damaged (I don't know how to get them all the
way out), reinstall the center one first.  Operate the lever and make
sure that it pushes and pulls the actuating rods.

Install one side.  You'll have to move reach in and line up the two screw
holes.  Push the lever (the one you're supposed to pull to open the door)
all the way down, then tighten the screws.  Rotate the latch up to
vertical.  Actually, since the tailgate is now down, you'll be rotating
it to horizontal.  Pull the lever and it should snap back.

If it doesn't, remove the two screws.  Rotate the metal piece so that the
hole that lined up with the top hole in the tailgate now lines up with
the bottom hole (and vice versa).  Put the screws in and try again.

Do the same thing to the other side.

(In the immortal words of the service manual) Reassemble in reverse
order.

Ray Drouillard