I was in a situation this year, where I was the Torah Reader for the Simchas Torah Day, but wasn't sure if they wanted me for the evening. It's a long walk for me. Anyway I was looking at what is read at night, and saw mention of Torat ha Musar. I beleive many communities do not read at all Simchas Torah night. So was wondering how it evolved from Torah Ha Musar to the practice of reading from ViZot HaBracha, 3 Aliyas.
Strictly speaking the Torah should be read only in the daytime. But since the scrolls have already been removed from the Ark for the processions, some argue that there ought to be a reading so that the Torahs have not been taken out in vain. The Rema says in his glosses to the Shulchan Aruch, “Each place follows its own custom”. Where the reading does take place, it is of the first five portions read on Simchat Torah morning and it is customary to use the Rosh HaShanah and Yom Kippur melody.