Functional labels provide a simple but very reusable way for defining the functionality of a system and for making use of that knowledge. Unlike more complex functional representation schemes, these labels can be efficiently linked to a behavioral simulator to interpret the simulation in a way that is meaningful to the user. They are also simple to specify, and highly reusable with different behavioral implementations of the system’s functions. The combination of functional labels and behavioral simulator can be employed for a variety of tasks - simulation, failure mode effects analysis (FMEA), sneak circuit analysis, design verification - producing results that are very valuable to engineers and presented in terms that are easily understood by them. The utility of functional labels is illustrated in this paper for the domain of car electrical systems, with links to a qualitative circuit simulator. In this domain, functional labels provide a powerful way of interpreting the behavior of the circuit simulator in terms an engineer can understand. This claim has been substantiated by the development of the FLAME application, a practical automated FMEA assistant in regular use at several automotive manufacturers.