Abstract: Electromagnetic relays are critical components in aerospace electronic control systems. Their coils, serving as the core of electromagnetic energy conversion, are prone to fatigue fracture due to stress concentration induced by manufacturing defects, which has become a major bottleneck limiting the reliability of aerospace equipment. This paper addresses a coil breakage failure of the KJZC-4M sealed relay in a specific aerospace module, systematically investigating the stress distribution characteristics of key manufacturing processes including coil winding, taping, and soldering. The underlying fracture failure mechanism is revealed under the coupled effect of process-induced stress and combined temperature-vibration stress in aerospace environments.Root cause analysis identifies that improper tension control during the coil taping process led to localized stress concentration in the enameled wire, acting as the primary trigger for fatigue crack initiation. Under prolonged energization and vibration loading, these cracks propagated and eventually resulted in coil open-circuit failure. Based on the identified failure mechanism, three targeted improvement measures are proposed: quantitative control of process parameters, integration of isolation and protection structures, and enhanced environmental stress screening. Life testing verified that the optimized relay achieved a coil service life exceeding 2500 hours, significantly surpassing the 1000-hour requirement specified in the national military standard. The findings provide practical engineering guidance for process optimization, reliability enhancement, and troubleshooting of similar failures in aerospace electromagnetic relays.