Sorry I noticed that the referenced document have reversed the pin numbering compared to the ethernet pin numbers.
It makes sense then.
The document lists the pins as:
Pin 8 (1) is NC (left pin looking down on flat side, orientation cable down)
Pin 7 (2) is O/F (12v+) 200mA capacity
Pin 6 (3)...
Just checking here... Pin 2 and 3 is listed as rs485 a and b pins in the Renogy document "Lithium Iron BMS Modbus Protocol v1.17"
Are you sure shorting them is ok?