I just bought a big 40.  it has this mysterious box right below the control panel.  it has a lid that lifts up and exposes the wiring inside.  the main welding cables go into it and there is a lever switch that seems to control where the welding current is going...there are welding lead lugs inside the box, and more welding cable going out of the box to the normal place that you would hook up the welding lugs on the side of the machine (same place as an SA-200).  that's all fine and dandy, except for these other little wires that are hooked to 3 of the welding terminals.  I trace these wires and they go to some kinda voltage regulator and relay that is wired to something else inside the machine. 

Is this some kinda constant voltage/constant current switch?  I've welded using the normal terminals and that all works fine.  I can't, for the life of me, figure this out and I don't wanna hook up any welding leads to something I don't know.