Toyota Repair: 1994 Toyota 4runner hub problem, electric solenoid, toyota 4runner

Question
Hello,
I have a 1994 4Runner (five speed) that appears to not be engaging the hubs.  When I shift into 4X4 mode (High or Low) it easily shifts into the desired position, but 4X4 light doesn't appear on dash.  I checked underneath the car and the front drive shaft is turning when I shift into 4X4 mode, but the front wheels are not engaged.  I recently had a head gasket replaced, but it seems unlikely that this would have any impact on this problem.  Is the engaging of the hubs mechanical or electrical?  Could a wire have been left disconnected?  There are no unusual noises coming from the transfer case.  Thank you very much for your help.
Avery

Answer
The engaging of the front differential is controlled by an actuator on the front differential, it is vacuum operated,and controlled by solenoids which send a vacuum signal to the actuator to move it and lock the differential so that the front wheels will turn, since there was a major repair recently I would suspect that the vacuum lines may not have been reconnected or an electric solenoid was not reconnected, have them recheck for this.