These are pictures of the inside of the Merkury Model: MI-BW-904 (mi-bw-904).
The control board with the ESP8266EX has the following identified (in this order) on two 4 pin connectors (all soldered) that connect it to the power board:
IO4. . . . . . . .IO13
IO14. . . . . . GND . . . . . . . . .Note: dots are just to provide space. No connection between these pins
IO5. . . . . . . .VIN
IO12. . . . . . .3.3
Hoping to understand what IOs are used for Tx and Rx
The bottom power board is marked EBP416-REV1.4
There is a 6 pin connector that connects the power board to the LED board.
IO04 and IO14 connect to the LED board.