Don't bother removing the door panel yet.

Do the test detailed on page 8N-111 of the Crossfire Service Manual.

This involves measuring the resistance of various components at the BCM, which is much easier to get to.

The time delay you notice is due to the internal power switching on the BCM, which has its own switching logic. Stop messing with it too much. If the motor rotor is shorted against the stator or motor body then you're probably pulling mucho amperage up to the limit of the solid-state switch (could be an H-bridge or maybe not).