Grumpy_Mike:
One with the correct ratio and the correct absolute values.
If you have a voltage and load it with a resistor, you have current. That is ohms law.A voltage divider is one of the most widely used configuration of resistors.
Or less formally
Voltage Dividers - SparkFun Learn
But since I have three PWM pins and one +12V where should I connect the other side of the voltage divider? To a common GND shared with the Arduino and the built in controller board (Which I would guess is using my PSU GND?)? I completely understand how a voltage divider works and functions so I do not need an explanation of that! I just wonder how I should wire it, maybe you could provide a drawing? If I understand somewhat correctly I should connect a voltage divider in between each PWM pin and a common GND and not wire anything to the +12V pin? If so I need to find the GND of the controller board, correct?
EDIT: Something lik this x3?