In 12th, or perhaps before engineering you cannot really tell of your interest in any subject. According to what I understand you must be having an inclination and likeability towards Automobiles. Situation may be completely different once you are in Institute and you may have certain other research interests. Hence, I would suggest you to pursue Mechanical Engineering, as it is a much broader field of Engineering with India's never finishing demand for Mechanical Engineers. This branch also has very good career scope and prospects in almost all sectors be it Industrial, Aerospace, Materials, Power or Technology and Automation, in both public and private enterprises.

In India itself, most of the PSUs, whether belonging to the Metal Industry like SAIL, NMDC, RINL, MOIL, BEML or Infrastructural Development and Energy/ Oil and Gas industry like NTPC, ONGC, IOCL, BPCL, HPCL as well as Public Research Organizations like DRDO, ISRO, BARC definitely have vacancies for Mechanical Engineers round the year through GATE and other respective entrance examinations.

For more information about Mechanical Engineering do follow the link below

https://www.careers360.com/courses/mechanical-engineering-course