We first develop techniques for identifying the configuration of a body assembly system. These techniques are essential because of the increasingly sophisticated hardware adopted in modern automotive assembly plants. Then we use these techniques to benchmark the system configurations of three different automotive body assembly lines. Then we analyze the system reliability of serial, parallel, and parallel-lines and serial-groups systems. Some results are the following: with constant machine reliability, an assembly system could become more reliable if it has more possible paths of material flow. A parallel system configuration has the maximum system redundancy, and its reliability is highest. A serial system configuration has only one path of material flow, so system shutdown cannot be avoided if any of its stations fail. A serial-groups system has a slightly higher reliability than a parallel-lines system has, and both of them are much more reliable than a serial system. If we want to increase the reliability of some critical processes, we can combine several tasks and then duplicate the lines to form a parallel system with not-so-expensive machines. We then analyze the same four configurations for their expected production and present these results also. The relationships between sheet metal assembly quality and different assembly system configurations are investigated. Four different assembly system configurations (serial, parallel, and parallel-lines and serial-groups system configurations) are designed to produce the same sheet metal product. With the same sources of variation, we simulate how the dimensional variation of assembled sheet metal parts is affected by different system configurations. "Mechanistic variation simulation" is used to analyze the variation stack-up of deformable sheet metal part assemblies. From the simulation results, we find that the more material-flow paths an assembly-system had, the distribution of its products' quality is wider. Also, the parts processed through more serial fixtures may have a higher mean deviation.