[Tom Line]

Is this with the robot enabled, or disabled?

If it's disabled, you have a short on the motor side of the motor controller, or the motor controller has failed internally somehow and is sending voltage through.

If it's disabled and running, pull the fuse. If the motor stops, it's likely you've got a faulty motor controller. If it continues, you have a short on the motor side of the motor controller.

If it's enabled, work backward from the motor.

Is the light on the motor controller changing color?

If it is, you know the the controller is getting a signal to run.

This may indicate your code is telling it to run, or your pwm cable is damaged or shorted. The next step is to either replace the pwm wire, or check what your code is outputting by looking at your dashboard for that particiular output.

This is all assuming that the wiring for the motor was done correctly.... it may be that someone miswired the motor directly to the power distribution board. That would also cause this condition.