“I don’t know anything about cars.” Uh, not exactly what you want to hear from the guy who’s going to lead General Motors when it emerges from bankruptcy protection later this summer. Former AT&T chief Edward E. Whitacre Jr. admits he’s not a car guy, but the man known as “Big Ed” figures business is business, and he was pretty good at it over a 43-year career. The White House is confident Whitacre will do fine, noting that Ford’s current CEO, Alan Mulally, came from Boeing. Still, taxpayers jumpy over the public investment in GM — $20 billion already and another $30 billion to come — must hope Whitacre studies up a bit before he officially takes over. GM can’t afford any more missteps.