power window motor or regulator?? how to test

Im going to help my dad fix the power windows on his car. I know its not an a body but i figured someone here might have the know how to get me in the right direction. Both front windows are not working on a 01 grand caravan. (stoped working at differant times). I am going to remove the door panel and try adding 12volts to make sure its the motor. Now if 12v does not make it go up and down, i am assuming it is the motor and not the switch. But how do i find out if i need a regulator or not?? Since they sell them with and without regulators?? What exactly does the regulator do?? I did have alot of knowledge on electrical. thanks for any info
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