In today's automotive development environment it is necessary to look at the totality of an automotive system. For this approach is necessary in order to optimize system designs for reliability, manufacturability and cost. Optimization in the case of the automotive system or subsystems, entails performing trade-off studies on the different components taking into account their interactions. In doing so it is necessary to employ a mixed domain simulation tool. In the case of the Cranking and Charging System electrical, mechanical and thermal domains must be co-simulated. The focus of this paper will be to show how a typical Cranking/Charging system can be analyzed and how the appropriate design decisions can be made.