Abstract: A multiplex information handling system for a vehicle has a number of transmitters and receivers all interconnected by a common power bus and signal bus. The transmitters transmit signals along the signal bus representing the operational state of control equipment or equipment controlled by that equipment and the receivers respond to and act on such signals to, for example, authorize the display of information received or the initiation of a control function. System management and supervision is provided, such that, where the transmission of certain signal states is made dependent upon the state of other signals in the system, this dependence can be overridden, for example, for vehicle servicing. Supervision also provides for certain urgent signals to be given priority over other signals.