THE Detroit headquarters of the big three American carmakers have long been insular places, wary of outsiders. Not without reason. In recent times, for example, Ron Zarrella, brought in from a contact-lens maker to run GM’s North American division, and Bob Nardelli, a DIY-chain boss who had a short reign in the boss’s chair at Chrysler, both came to be seen as unfortunate choices.So it is notable that the recent turnarounds of all three are taking place under bosses who are neither company lifers nor even “car guys”. Ford’s Alan Mulally came from Boeing, a planemaker; GM’s Dan Akerson is a former telecoms boss; and Sergio Marchionne of Chrysler joined its Italian parent, Fiat, from SGS, a Swiss inspection firm.The three have quite distinctive management styles. Mr Mulally gives hugs, and means it. He is a sort of “demanding cheerleader”, a boss you want to do your best to please, no blame-thrower but no soft touch either. He has swept aside a culture of politicking and back-covering among Ford executives by making it possible for them to own up to problems….