The endstop pullups on Sanguinololu aren't on the board. The AVR has switchable pullups on the I/O pins, which is why leaving the pin disconnected doesn't help.
In Marlin Configuration.h, you need to uncomment "#define ENDSTOPPULLUPS" to make this happen. Also make sure the correct board type is selected (62 if not using external fan control). Not sure about Sprinter.
In Marlin Configuration.h, you need to uncomment "#define ENDSTOPPULLUPS" to make this happen. Also make sure the correct board type is selected (62 if not using external fan control). Not sure about Sprinter.