"Joe Peters" wrote
There is a small switch that screws into the top of the T-case. It is
> roughly the size of a knock sensor, for comparison. At one end of this
> switch (the end inside the case), there is a spring-loaded steel ball.
> At the other end, there are three vacuum fittings, and vacuum lines
> running up to the engine compartment. Does anyone know what the hell
> this is, and what it does...
When you shift into 4 wheel drive, this switch applies vacuum to a vacuum actuator sitting under the battery which in turn shifts the front axle into engagement thru a cable.
Ian