I think the Joiner looks just like a cable wiring with pins 1,4, and 5 straight thru. And pins 2 and 3 crossed over. Then there is a resistor and LED across 5V which I'm calling pin 1 and GND pin 5.
But the B Joiner has a couple diodes and a power input. A boost of 5 vdc? and what...some protection against back feeding the power?