I am using an ULN2003 to control a unipolar stepper motor from my PIC18F45K20. When I only connect the one 12V power cable (Red) the stepper motor works in full step. However, when I connect the other 12V cable the motor stops and has a high pitch noise and the outputs on all the PIC ports go low. So in conclusion when I connect this one specific red cable, nothing works. I tried another stepper motor (same model) the same happens. Any suggestions what it could be?
My motor is similar to this one I found on the web.