The standard instrument cluster contains a microprocessor. The instrument cluster microprocessor communicates with other class 2 modules in the vehicle over the class 2 serial data line. The instrument cluster also communicates with other devices on the vehicle using dedicated circuits to specific components and sensors. The instrument cluster will display the results of the information it receives by the use of lamps, indicators, gauges and illuminated displays in the instrument cluster. Some of the displays and gauges are operated directly by external sources (devices or other modules). Other displays are operated under software control of the instrument cluster. As the instrument cluster microprocessor processes its internal software, the instrument cluster continuously monitors and processes class 2 serial data. This is so the instrument cluster can display the correct value of the gauges, the correct state of the indicators and lamps. The high beam, turn signals, and the panel lamps are the only replaceable bulbs in the instrument cluster.