Thank you for the quick reply and great pictures. Your experience and wisdom are greatly appreciated!
I now have the parking brake module out and I have the motor out of the assembly and there are signs of motor burnout/failure. First, there is black residue in the shape of an oval on the white gear housing that matches exactly to the mating metal slot on the front of the motor face (the motor side with the shaft and gear). Second, there is additional black residue located on the outside of the gear housing away from the motor interface. I assume it was blown inside the module, when the motor was beginning to fail and burning out. In addition, I smelled the familiar electrical burnout from the motor vents. Third, when I tested the motor. I disconnected the motor positive and negative leads. I applied 5V, from an adjustable DC power supply, to the positive side of the motor blade and connected the negative lead from the power supply to the negative motor blade. The motor worked a couple of times but then stopped. I could not revive the motor, even with 15 amps at 5V.
I separated the motor from the gear train assembly and provided 5V, which took ~10 amps to turn the motor shaft and gear (motor gear not connected to gear train assembly). From my understanding, to turn the motor, it should take ~ 5 amps at 5V. I believe the evidence shows the motor is in a decline to failure and probably didn't have enough torque to pull the parking brake cables and actuate the parking brake in the drum brake. Would you agree or is there another test you would recommend?
I have ordered a new motor from Amazon, however it will take 2-3 weeks to arrive. So please let me know if you have another test for the motor.
w221 Parking Brake Motor Senyar Parking Brake Actuator Motor,Car Handbrake Module Motor for S Class W221 2006-2013
I will add an update when I get the new motor and install it into the parking brake module.
Thanks again Jagpilot!