Charging system problem on a 2004 Saturn ion after replacing starter.

[jusmetana]

I have a 2004 Saturn Ion that the starter went out on so I bought a new starter for a 2004 Ion after replacing it the battery light stayed on. I thought it was the battery itself because it was so old so with a new battery the light still stayed on. Then I buy a used alternator that came off a 2004 Saturn Ion and serpentine belt and still the battery light is on. I really need help with this, myself and a 5 yr old have been stranded 2x's and we live 20 miles from town.