||What I believe is irrelevant; I could agree absolutely with all your moral principles and yet still honestly maintain that there is no such thing as an 'set of universal moral principles'.
What you believe is highly relevant and it's not really about agreeing with my moral principles, at least not to begin with. If you personally do not believe that you have a sense of right and wrong, a sense of what you ought to do (though you may not follow it most of the time) which is separate and distinct from your herd or survival instincts then it is irrelevant whether it is universal or not. End of discussion. You disagree with me, no problems at all.
If you agree that yes, you have this "thing", then can we can consider if this "thing" is indeed common to everyone, whether it is funcamental law of man or simply something we learn.
This is hard to do with pre-literate societies. In such situations you have to examine their collective myths, taboos, and sense of justice
Well yes, with pre-literate societies it is harder to pinpoint what their moral teaching was because have a lot less information to go on. We need to study things apart from explicit writings per se. However, you can still identify a moral teaching with enough study of the history and context of the society and the particular teaching mechanism they used (be that via symbols on a cave, their customs, rituals or whatever).
along with how the society operates.
No! How the society actually operates may have nothing to do with what their moral teaching is. You can't use the actual behaviour of a society, you need to use their teachings -- what they considered decent behaviour or Right Morality - not how they put it into practice. The same thing applies today - we rarely behave as we think we ought to, despite what we may say and write. If you were to look around the world today, you would hardly think that we have a moral law inside us would you! That's why, if we didn't have ourselves as a starting point, if we were observing man as a third party, we would have no reason to believe a moral law exists at all.
We live in a particular society, at a partcular point in time and have grown up imbibed in that societies norms. These morals are taught and learnt.
OK, let me ask again, do you think it possible for one society or person to be more moral than another? What would you be basing this "more" on?
From what I have read, you seem to be a moral relativist - that nobodies behaviour can be judged as "right" or "wrong" as such, it's all just relative. Therefore you have no right to condemn the Nazis, the Crusaders or child rapists, after all, who are you to say what is right and wrong behaviour.
If you say with respect to a question like "Why ought I to be unselfish, why ought I not kill someone" that "Because it is good for society", then I may ask "Why should I care what's good for society except when it happens to pay me personally?" Then you might say, "Because you ought to be unselfish" - which simply gets us back to the beginning. We have not progressed.
Trying to benefit society (by being unselfish) is one of the things that decent behaviour consists of; all you are really saying is that decent behaviour is decent behaviour.
Do you believe in the same moral code?
Well again, since my sense of right and wrong cannot be identified as always following a given instinct (e.g. fighting, sex, survival). I can't give a definitive yes and no for every instance. Actions that are blatently wrong in some context may be right in another. I can say that yes, I would think that abortion or denying someone the right to die can be "wrong" but I can also imagine times when it might be right (if the woman was raped, if someone was high on drugs when they decided they wanted to die). You can't pinpoint right and wrong as always executing a particular action. You can however take it to a higher level and identify a common theme of right and wrong (e.g. unselfishness, fair play, honesty, courage).