There seems to be some confusion with ground and polarity. Ground, by itself, does not have a polarity until it is connected to the battery. Regardless what polarity ground is assigned, any electrical device that is polarity sensitive needs to be connected positive to positive, negative to negative. Where it gets tricky is when the case of the device is also connected electrically to one of the inputs or outputs. A simple test with a ohm meter will tell you if any of the leads are connected to the case.