An electromechanical switching device ensures automatic selected polarity interconnection between terminals of two power sources. A double pole double throw (DPDT) switch has three pairs of contacts. A first pair of leads connect to two pairs of contacts in a manner that reverses polarity when switched, while a second pair of leads connect to the other pair of contacts. A switch controller employs a plurality of coils in electrical communication with the two pairs of leads. The coils are arranged and configured so that, when the two pairs of leads are connected to the respective power sources, the coils cause an actuator to move the switch automatically into the correct polarity state regardless of the connections of the leads. The invention is described as a battery jumper cable and to automatically connect like terminals of a pair of batteries. The invention encompasses the method of this device.