Expert: Mike Evans - 1/15/2010

Question
my car wont start after somebody put on a new alternator, i want to know if the alternator needs to be polarized first?

Answer
    Alternators do not have to be polarized.  That was something you did to generators, and then only if you were replacing the regulator at the same time.  In a modern car, though, the battery needs to be fully charged in order for the alternator to work.  So, you need to take out the battery and hook it up to a charger until it is fully charged, then put it back in.  If the battery light still comes on when the car is started and running, then the battery is bad, too.  An alternator will not charge a flat battery by itself, it needs some help.