Convert voltage controlled switch into ngspice
This link here has some info.
If your trying to translate models

First make sure they are an equivalent model.


Design a simple test spice file that will test the model with a voltage source.  
Test the model that you want to use in a different spice package so you know what the correct result is 
Test the SW model and 'play around' with it until you get the same result.


It will take some work, but somebody's got to do it.