I just placed an order for a BLTouch.

I also did a trace of the pin-outs on the ATMEGA2560 board for the Z_MIN Axis, image is attached, in case the image is not clear, following are details starting from the top:
- top pin: connects to the ATMEGA2560 chip
- 2nd pin: GND
- 3rd pin: GND
- 4th pin: +5V

Hope this helps

https://photos.smugmug.com/3D-Printe...3/Z-MIN-X3.jpg