How to make a paper's author willing to help me with his source code like a semi-supervisor? I am really in trouble. I am doing my MA thesis on wireless sensor networks, and I have a source code with more than 16 files and each one more than 5000 lines. It's very complex and has no documentation and that source code is all I have to do my thesis.

I am totally dependent on the author's help. I have been working on his code for almost three months now but because of the lack of documentation, my progress is very very slow. Also, my supervisor has no knowledge of the concept or the source code, and I have no time to change the supervisor, concept or source code.

So, how I can tell the author of the code please help me? How can I make him willing to help? What should I tell him in the emails? 

By the way, he answered my questions in the past. I asked three questions and he answered them. I've previously asked about the etiquette of repeated emails to him in this question.

But I need his help like semi-supervisor. By the way he is a kind person as far as I know.
No one can really 'make' anyone willing to help you.  However, some things to consider that may convince the author to help.  In your email communications:


demonstrate your understanding of the source code. 
Be specific in what you ask - don't do the "I don't get any of this" type of message.  Use your understanding, research and testing to help focus your questions.


Make sure you have your understandings and questions ready before you email, do not send multiple emails before they have a chance to reply and try and put most, if not all of your questions in a single email.  Be patient when waiting for a reply and be courteous and thankful for information provided.  

Have your supervisor/advisor look over your questions before sending it (if you're unsure).

Remember, most of all, the author is under no obligation to even reply, and definitely not under any obligation to do your work for you. Bear in mind that they will have time-taking obligations and duties that take priority.