Toyota Repair: 1994 4 runner 4X4 wont engage, vacuum lines, soft dirt

Question
My 94 SR5 4 runner, 120K miles, with A.D.D. won't engage. The drive line to the front diff turns when the lever is placed in 4hi or 4low and does not turn when in 2hi, but no 4X4 light on the dash and no 4X4.  I tried driving in soft dirt up hill to see if it was just the light, the rear wheels would spin but not the front. The light does not come on when you turn on the ignition as the other dash lights do (don't know if is suppose to or not). I have checked all the fuses and wiring under the dash and hood.  Is the A.D.D. electrically engaged or vacuum?  The vehicle sat for a couple of months without use and the battery discharged.  I charged it and it seemed okay and I can't recall if the 4X4 has worked after that or not.  Thanks for your time  Walt

Answer
There is a vacuum controlled actuator on the front differential, the switch that turns the 4x4 light on is in the front differential so what is happening is that the front differential is not locking, check the vacuum lines from the VSV under the hood to the actuator, if they are connected remove the actuator and test it with a vacuum pump, a common problem is that the steel vacuum connections on the actuator get clooged up with rust and sometimes can be cleaned out, if not then the actuator should be replaced.