Old lights and new lights preachers both followed protestantism. how did the two differ?

The answer to your question is both New Lights and Old Lights ideologies were initially the same, but they split up because the New Lights has become inspired by new ideas and beliefs (especially about sins and penance) spreading through New England, while Old Lights were more traditional. It took place during the First Great Awakening, a new evangelical movement taking place mostly in American colonies in 1730s and 40s.

I did the same thing.