I was a bit confused at the operation until they clarified. You provide the desired voltage to switch on Vcc (e.g., 5 volt, 12 volt, ...) and the ground. These wires should be sufficient to carry the desired load current.
You provide a switch signal (e.g., 5 volt or 3.3 volt) to the sw signal to close the switch and gnd to open the switch. The LED turns on when switch is closed.
When 5 volt or 3.3 volt are provided, the neg output connection is shorted to ground thereby completing the output circuit.
I wondered what would happen if I applied 110 volt ac. I found that a 150 watt bulb dimmed. No damage though so this product is robust.