ASCII gateway to in-vehicle system provides bi-directional translation between multiplexed motor vehicle networks and industrial control and monitoring devices. Integrated hardware and software components provide data communications between motor vehicle electronic control module networks and RS-232 serial ASCII-text capable device, for industrial control and/or industrial automation application in manufacturing or assembly operations. Communications networks (CAN, SAE or ISO protocols) implemented inside motor vehicles pass data between electronic control modules that control operation of important vehicle components like engine, transmission and brake systems, have their messages converted to RS-232 serial ASCII-text; and from RS-232 serial ASCII-text converted to motor vehicle communications network by the system. Messages to monitor and/or control vehicle networks are generated by a serial ASCII-test capable device. Multiple vehicle protocols are supported by the system. The system translates between RS-232 serial ASCII-text message generated or received by a device and the vehicle network.