91 Jimmy rear hatch broken

I have a 91 GMC Jimmy. It runs fine but body is in terrible, terrible shape. Recently, the rear hatch/tailgate handle just broke off. I don't care about not having the locking latch anymore but I would like to able to open and close the rear gate. I made a water-tight plug that I can insert and remove from the hole to keep water out and I can actuate the glass window release mechanism with my finger (through the hole where the handle used to sit) but I can not find the mechanism for releasing the lower tailgate door. Does anyone know how I can locate and release this mechanism easily? I can't find any schematics or manuals that show the interior door latch mechanism.