Neither of the doors or hatch on my '98 ZR2 Blazer I just picked up would lock electrically. I could hear the actuators unlock but not lock. After searching all the posts here that I could find on the topic and pouring through the owner's manual that was still in the glove box, finding that a previous owner had installed an Avital 3300 security system, I figured that starting with the security system would be the place to start since I didn't have the primary remote to operate it.
I looked up the Avital system on the internet to know what I was looking for. After finally locating the Avital module I simply unplugged the approximately 9 connections going to it. All the electric locks work properly now. So far it seems that unplugging the module has not had any ill effects but I haven't checked everything yet. I'm very thankful that the first owner documented all that was done and that was still in the vehicle, also thankful to all the posts here on this forum.