You can connect the Power Functions motor to the EV3 with a LEGO 8528 cable and a LEGO 8886 cable.
In addition to the cables, you need to know how to trick the software. You can use the unregulated motor block, but it will stop after a short time (1 second or so). You have to constantly change the speed to keep the motor powered.
Here is a simple example to run the motor at 75% of full power:
Using a single unregulated motor in a block like this won't work because the power value does not change. It seems that changing the power value is what resets the timeout on the EV3.