If it was a blown fuse, you should get 0 V. You might test the theory by removing the fuse. More likely it's a bad wire. Try a different ground than the one of the lighter, like touch bare metal with the negative pole of your meter. You should get the same result, but if you get 12-14V, then you know it's the ground wire that's at fault. If not, the positive wire could be corroded somewhere (same goes for negative). Check also to see that you get 12-14V at the fuse itself. That could eliminate some things.
And also, it's possible the lighter is itself corroded, needs cleaning, bad or else. It's worth it to remove it and test at the wires because some of the above could apply to the lighter being at fault.