I have a 93 Chevy K1500. The 4 wheel drive recently stopped working. The lights come on when I put the manual shift into 4 hi. I replaced the thermal actuator with the electrical one and wired it in. When I put it into 4 wheel I can hear the actuator sound like it is engaging. I don't think, therefore, that the actuator is the problem. Any ideas? If not can you give me a basic rundown of how the four wheel drive engages? Any help is appreciated.