I have a 1995 gmc sierra and the 4wd is not working. I changed the front diff actuator but it did not solve the problem. The actuator is good (tried it in a buddy's truck) the front drive shaft does spin when the transfer case is engaged (I can also hear the tranfercase gear down). I did get the tranmission rebuilt a couple of months ago and after this is when I noticed it was not working. 4x4 lights do not illuminate when I engage into 4hi or low (I have a floor shifter). I tested the wire that connects to the actuator with a voltmeter and it showed no charge. I then traced the wire to the top of the transfercase and tested both the end of the wire and also where it plugs into the transfer case...no charge shown.