I am trying to find information on how to replace a tailgate lock actuator for a 2000 Jeep Grand Cherokee

first is diagnosis.
you examine and test it. to see if its electrical or mech. failure.
and once discovered that follow that to logical conclusions.

a weak door lock actuator that locks the rear tailgate

Sounds like the lock actuator in the tailgate has gone bad. I have a 1999 that had the same problem. Its about a 120 part from the chrysler dealership and involves taking the interior trim off the tailgate to repair.

replace the struts.

it sounds as if there is a wire or the door lock actuator is bad on the back door as well as the tailgate give these websites a try www.alldatadiy.com and www.autozone.com if all fails stop by your local Jeep dealership in the parts department and they be able to print you off the pictures and diagrams you will need wish you the best of luck Michigan Man.

tHEY MECHCANISIMS IN THEM RUST UP AND DONT LIKE TO WORK TRY REMOVING INNER PART OF TAIL GATE AND SPRAY WITH dw-40 and move them till they become free its basically rods that do the work of opening and closing sorry bout caps

the most likely failure is the tailgate lock actuator, the tailgate will have to be taken apart from inside (very difficult)

I think you will find a small hatch on the inside of the tailgate,this will allow you access to unlock the tailgate.Possibly the lock actuator has failed.

The lock accuator on the tailgate is bad.

I don't think you need a wiring diagram.
Jeep had alot of problems with the lock accuator in the tailgate.