Window roll up module in Civic simple

When the unit sends 12v out to lift/drop the windows, it uses the original ground from the vehicle. ( as the motor lies on a ground when they arent being used) It only feeds one side of the motor wire at a time. Not both. From what i can make out, you were thinking that it would feed a ground to one side of the motor wire and a 12v live to the other. But since the battery you were using, wasnt part of the cars electrical circuit then it wouldnt show up. For it to work, you would have to connect the ground terminal on the second battery to a ground point on the vehicle so that the circuit was complete.