The Controller allows the triggered input through the plastic logic card to sellect your direction contactors, and also allows the system to trigger the thyristors within the aluminium block which in turn allows your motors to turn and drive the truck, if there is a fault condition the system has a fail safe circuit in the card which will trip out the contactors to prevent any serious damage or injury. Traction control is in reference to the pulsomatic system.

As for the switches on the steer hub, not sure but sounds like your truck is probably twin drive with 2 motors, and the switches probably drop out one of the motors when in one lock and vice versa. I know the system but am not familiar with the actual truck sorry.