Hey Yar-El, I'm not sure if this will answer your question directly, but even in the Old Testament I believe there are references/hints towards the concept of Trinity later in the Bible. Take for example this
passage, seems to hint towards the crucifixion. This
passage is even clearer about there being multiple persons in the Godhead, considering one of the 10 commandments says not to have any other god and the monotheistic nature of the rest of the Old Testament.