These particular BMS units are even easier because they are common port BMS units. Meaning you can charge and discharge through the same wire. B- always go to battery main negative. C- then becomes your new main negative that will connect for charge and discharge. Your main positive doesn t go through the BMS. Look at a BMS like a smart in-line fuse on the negative of the battery. Balance leads start with the black wire on the negative and then each wire in order goes to series 1 positive, series 2 positive, series 3 positive, etc. That is why the balance leads always have 1 extra wire than there are numbers of series. A 4s BMS, for example, will have 5 balance wires. One for the main negative and 4 for the positive of each series.