Controll a treadmill w/ bad display

I am trying to use an arduino to control a treadmill that has a upper control unit that is not working consistently (occasionally it will work, but now it is out more often than not). The treadmill has a lower control board with an 8 pin connector and a very simple schematic for those 8-pins (the only documentation, it was on a piece of paper under the motor cover). There are 2 ground pins, one 8-14VDC pin, one 0-5VDC PWM, one for the speed sensor (hall effect), and one for Elevation up, Down, and Elevation rotations.

My first try was to simply control the motor using the same interface. i used the power from the motor controller to power the arduino (so we all have the same grounds), and i made a simple loop that uses Pin 3 for PWM to control the motor (analogWrite), the loop goes from 0 - 125 in increments of 5 every 15 seconds. The arduino powers up, and every 15 seconds it is telling me it is writing a new value to Pin 3, but nothing happens to the motor. I realize that this isn't much to go on, and I don't have an o-scope. Any help, or anyone done something similar?

Thanks.

I tried sending it voltages directly (using the 5VDC and the 3.3VDC output from the arduino) with no response from the treadmill motor.

I am guessing that the info was for someone using a multimeter to test for voltage (it does specifically say "PWM") it has a note that some multimeters will not read the full voltage (I am guessing because a meter does averaging, or doesn't sample or display fast enough)