As a previous post mentioned up above somewhere, there are two wires on the front of the axle that operate the 4WD light on the dash. I made the mistake of not unplugging the connector when I did my body lift, and broke the wires. When they touched together, I got the clicking noise in the dash. I cut them off and taped them up, and don't use the wires to the light now. The 4x4 operates normally without them, since all they seem to do is operate the dash light. If you look at the axle from the front, you should see the connector just to the right of the differential. Check the connection. (If it's not that, it must be something else with the vacuum line or internal, in which case the 4x4 probably doesn't work.-can't help there).