I recently purchased 2000 GMC K2500 with a 5.7 Vortec, AT and manual 4WD shifter. While I am able to shift into 4HI but the light indicating 4WD does not light. I removed the front axel actuator, purchased a new one and neither one will stroke either in the differential or out. I looked at the transfer case and am able to see two sensors or switches. Two questions:

• The plug for the front axel actuator is five pin. Does anyone have a schematic that shows what each contact does?
• Does either of the two sensors or switches send a signal to the front axel actuator and could this be the source of my problem?

Any help would be appreciated. Thanks