2006 Crown Vic rear lock help

Hey everyone, I was wondering if anybody has tips on what parts are typically missing from inside the rear doors that disables the locks. I've seen some videos on youtube, but they vary as far as fixes. Has anyone had it as simple as replacing the rod to the door latch? Not much of a car guy as this is my very first. Trying not to have to take it to a shop, 'cause I've seen quotes around $300 just for the damn actuator. Any help would be awesome. Thanks,

Zach