Design and testing of J-1850 multiplex communications networks requires a range of support tools which facilitate the process from initial concept, thru bench development and vehicle implementation. In the early stages of design, vehicle features, I/O, and functionality of the various option mixes must be mapped into modules, and communications requirements and message strategy between modules defined and simulated. When modules become available, a means of emulating network traffic on the bus is required in order to evaluate actual module responses. Network monitoring and diagnostic tools are also necessary at both low and high detail levels. This discussion will cover several multiplex design and analysis tools which are under development at Ford.