A new set of terms and conditions for OnStar, the General Motors-supported safety and connectivity system, is generating privacy concerns among some subscribers, many of whom have been historically sensitive to the potential for abuse. For years, some G.M. car and truck owners have posted elaborate instructions to Internet forums and user groups detailing how to disable built-in OnStar equipment to prevent any tracking of their vehicles. Last week, OnStar sent e-mails notifying customers of changes in the company’s policies. Some customers say two changes in those terms were of particular concern from the standpoint of privacy. The first regards what ...