Charging 4s 18650 with one iMax B6
I assembled a battery pack myself.

Your schematic is not correct, because the chargers expect a balancing connector with n+1 contacts: negative plus positive of each element. Basically the 5 wires from your battery pack are ALL needed for the balance.

In addition, you have to connect to the charger also the (two additional) leads you use for the normal use.

See the image (Lipo or LiIon, doesn't matter).