4x4 Actuator

[GMCHORSHAM]

I cannot get my truck to go into FWD, I have had
problems in the past, which seem to be intermittent.After servicing my truck on the weekend, I thought that I would check this out.
I had noticed that the FWD indicator light doesn't illuminate when selecting FWD, couldn't hear any actuation (meshing) when selecting either.
I removed the actuator from the housing, replugged the harness, and selected FWD, as a test
to see if the actuator was working. However
nothing happened.
Can these actuators be bench tested, any tips on doing this would be appreciated. Also I removed what appeared to be a relay unit, can these be tested also.
By using a straight bladed driver, I was able to insert this into the actuator housing and move
the gearing 1/2-3/4 inch, so I am assuming that this part is ok. Any tips are appreciated or should I just go with the Posi-lok manual system
and scrap the electrical actuator.
I have also read that their is an updated replacement actuator for the 1994, can anybody provide some details on this part type- ect.
Any details are much appreciated.
Have Fun, Safely.
Rod.