Check the "floppy drive A pin out" table on this page
. We're interested in:
10: 0=motor enable drive 0 (when at 0v the motor will be spinning)
14: 0=drive select 0 (so that step and direction commands go to drive0)
18: direction (which direction to move the stepper)
20: step (pulse this to make a step)
Note that all the odd pins are ground.
Wire up the floppy cable like this:
floppy pin 14 -> floppy pin 13 (this selects drive 0 as we tie it low by connecting to ground on pin 13)
floppy pin 1 -> arduino ground (we need to connect the ground of the arduino and the ground of the floppy)
floppy pin 10 -> arduino pin 4 (platter motor)
floppy pin 18 -> arduino pin 3 (direction)
floppy pin 20 -> arduino pin 6 (step)
We also need to power the drive. I measured current draw and it peaked at 300mA. I did some research and it seems safe to power this from the 5v pin of the Arduino. USB has a maximum rating of 500mA for current draw and we're safely within that limit.
If you have a floppy power cable then connect the Arduino ground to a black and Arduino 5v pin to the red cable. Otherwise you'll need to work out which is pin 1 (it might be marked on the drive) and then use the table floppy power connector
to know which pins to connect where; pin1: 5v, pin2 or 3: ground.
Turn on the power and check you get a light coming on somewhere at the front of the drive.