The stator turn-to-turn short circuit is an important type of fault in automotive claw-pole generators. In a typical vehicle electric power system, the built-in rectifier of the generator makes it difficult to access the ac current or voltage information, rendering conventional sequence-component-based fault-detection methods useless. To detect such fault using only the available sensor information, a dynamic model of the claw-pole generator with stator turn faults is derived in this paper to analyze how the fault would interact with the connected battery and the static full-bridge rectifier and how it would affect the generator's output voltage and current. It is found that, in the rectified generator output current, the harmonic at one-third of the rectifier ripple frequency is a robust signature of the stator turn fault. The performance of the stator turn-fault detector is demonstrated by extensive experimental results. Although the fault detector is originally proposed for claw-pole generators, it is also applicable to most polyphase ac generators with a dc-link rectifier.