The global auto industry had plenty to worry about in 2014 as it navigated shifting technological and economic tides, the usual brutal forces of competition and consolidation, and a host of other threats: volatile fuel prices, the technological arms race toward battery- and hydrogen-electric vehicles, maturing developed markets, the rise of mobility-sharing apps such as Uber and the specter of self-driving cars. But an even greater horror stalked the auto industry this year, leaving a trail of dead customers, baffled executives and livid regulators: Takata's exploding air bags.