A teen was arrested Thursday for allegedly setting a sleeping homeless man on fire on board a train passing through Midtown this week, law enforcement sources said. Hiram Carrero, 18, of Harlem, was charged with attempted murder after he was picked up in the East Village for the harrowing Monday attack, sources said. The unhinged firebug stepped into a No. 3 train approaching 34th Street-Penn Station just after 3 a.m. and set the snoozing 56-year-old victim ablaze, cops said.