Mating a pair of electric connectors is one of the most important steps in a robotic wiring harness assembly system. A class of piecewise linear force models is proposed to describe both the successful and the faulty mating processes of connectors via an elaborate analysis of forces during different phases. The corresponding parameter estimation method of this model is also presented by adapting regular least-square estimation methods. A hierarchical fuzzy pattern matching multidensity classifier is proposed to realize fault detection and diagnosis for the mating process. This classifier shows good performance in diagnosis. A tyical type of connectors is investigated in this paper. The results. p. P can easily be extended to other types. The effectiveness of proposed methods is finally confirmed through experiments.