I have tried three SD modules (cheap Chinese no name) two with six pins and one with a 7th 3.3V pin.
None of the examples in the SD library can initialize any of the modules and report "Initialization failed!" which is the condition
SD.begin(4) == 0. I have checked the wiring connections to the Mega multiple times. I have also swapped the MISO/MOSI. No LED (if any) lights on the module.
The pins are the driver defaults 4 CS, 11 MOSI, 12 MISO, 13 CLK .
I understand that these modules operate at 3.3V, but also accept a 5V MCU, as they have a VCC pin, and the description appears to say it will work with any Arduino. They come with a LDO regulator. Link is to the description of the module. Any help will be greatly appreciated.