Donut Mechanic

This post was very helpful. Thanks to all who contributed. I wanted to add a bit that I found while troubleshooting why my 1996 K2500 would not engage the 4wd. I went through all the troubleshooting and finally found the brown wire going from the starter to the actuator on the front axle was melted through. I am guessing this was rubbing in the exhaust. I fixed this and mine took right off. The brown wire on the actuator plug should have 12 vdc constantly. The blue should get peer from the switch on top of the transfer case while in 4wd. The black wire is a ground. Hope this helps.