MSD Power Grid Ignition System Controller 4-Connector CAN-Bus Hub. This hub will allow users of the Power Grid System Controller to connect other MSD modules to the system for added features. The hub uses CAN-Bus technology that can be stacked so that racers will never run out of spot to plug in modules. Each hub has 4 plug in points with a single output so that one hub can be plugged into another. To add modules to the system, builders simply plug in the 4-Connector CAN-Bus Hub to the System Controller and then plug the modules into the Hub. The CAN-Bus Hub is required to plug in any modules .