I'm upgrading to MKS 1.3 from ramps 1.4. When I put SD card in the slot, and power up the board, only one light comes on. The one closest to the SD card reader end. In this state I cannot communicate with the printer from ponterface and SD card does not mount in my MAC. I erased and reformatted the card to FAT 32 to try to solve this. It didn't work.
With the SD card out the board boots and behaves normally ... mostly. See my other question about endstops.