As it says, the actuator on the front axle of my 90 k1500 is not engaging when I pull the lever to 4wd. I can see the front driveshaft turning, so the transfer case is good. I know its an electrical problem. The light in the cab for 4wd will come on every once in a while, but will turn off again in a few seconds of driving in 4wd. What are the common spots to see problems with this system's electrical?