Don't trial and error a BMS - PLEASE!.
B1 is the battery closest to the negative terminal (ie. its negative terminal is the pack negative). B12's positive terminal is the pack's positive terminal.
Get a multimeter and work back. Easy. B1 will be negative(0V), B2 will be 3.2V, B3 = 6.4V, B4 = 9.6V - all voltages are relative to pack negative terminal and approximate.
If you get stuck, tell me how may pins on your battery balance connector and I can help you out.
GNG offroad build on Craftworks DHR with 12S2P lipo. Light, balanced, powerful, able to climb a tree.
Project Vectrii (2) - status - Finished. Nope. 38S Leaf cells are next. Now have 2 of them - Averages 50Wh/Klm