Brother Earl,
arguably one of the most important non-canonical books of the Faith...try this for starters, its an 1822 507 page edition on Google, for free.
http://books.google.com/books?id=5ukDAAAAYAAJ&printsec=frontcover&dq=david+brainerd&hl=en&ei=PAwtTcDoJsWqlAfut_DXCw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CDUQ6AEwAw#v=onepage&q&f=false
i know the edition you're talking of, i THINK Harvard Press put it out recently, it was 600 pages...i didnt have the money at the time. i'm searching for you.......i assumed you've read the modern abridged reprints?
the "2nd diary" you reference may be the whole unabridged diaries, and various letters. There's a brother that puts out a CD computer disc called "The Revival Library", a few of David's letters are on that as well.
David is a sweet soul.....as you know he suffered mightily from melancholia, what we now call depression....who doesnt?
sweet soul, thank God Jon Edwards talked David into the wisdom of leaving his diaries for print as David lay on his death bed....the beauty is, when he wrote them, pouring his heart and soul out, he was only writing for an audience of One....that's what makes his diaries so powerful...they're real, authentic and powerful in their weakness.
i'll look more. neil