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In a DC circuit, current flows in one direction: from the positive side of the power source, through the load, to the negative side of the power source.
To switch the load, you can place the switch either in front of the load (on the positive leg of the circuit) or behind the load (on the negative leg).
Sourcing—The sourcing module goes in front of the load. Use a sourcing module when all loads can use the same power supply and all have a common connection to the negative side of the DC power source (0 VDC).
SNAP sourcing modules (lifetime warranty):
Sinking—The sinking module goes behind the load. Use a sinking module when all loads have power connected already, and you need to run one line back to the negative side of the power source.
SNAP sinking modules (lifetime warranty):
IMPORTANT: For inductive loads, make sure to place a commutating diode across the circuit in front of the inductive load. For diagrams, see the sourcing or sinking module's data sheet: