If you tapped 12v for example, from part of the pack by bypassing the bms, you will drive the pack horribly out of balance. This can overwork and fry your bms. So your lights need to run on pack voltage through the bms, or on a voltage converter that runs through the bms.
CA, pre charge, etc run through the bms.
Always through the bms, until you have an emergency where the bms died. Then, very carefully, you could run without. But only as a last ditch thing.
You could tap you pack for very very small draw stuff, like charge your phone. but not much more.