Ready to go out USPS Monday.
The three plugs are wired pin to pin to connect cells in parallel. Connect only to modules that are connected +to+ and -to-. To insure similar voltages.
It will work the same connected to 1, 2, or, 3 modules.
Bare boards are fragile and static sensitive.
The other bms and balancers use similar harness.
If the wires leave the plug straight up, it fits easily. Don’t force it and bend pins in the socket.
If it isn’t to your liking, send it back. At a minimum you will see how the harness works. Any number can be connected together.