The NX3DV3899 is double-pole double-throw (DPDT) analog data switch with dual channel intended for use as an analog or digital multiplexer/demultiplexer. This device ...
As you can see in the schematic the 12V battery (or use other voltages) is connected with the plus at terminal T1 and minus at terminal T2. The contact 1 and 4 are connected together as 2 and 3 are ...