Review on 🚚 EHDIS 12V 120A 4 Pin Car Relay Black Box Battery Set for Heavy Vehicles - Perfect for Trucks, Excavators, Vans, Boats, and More! by Monty Barganier

I used this to turn on the inverter in my work van. I wanted the inverter to be connected to an accessory powered switch so we couldn't accidentally leave something connected and drain the battery. Works flawlessly. I disconnected power to the relay from the ignition source and applied battery power to the inverter through the relay. Even if the switch is on, the inverter will turn off when the van is turned off. You need to ground the bottom of the relay. Mine didn't have a schematic, but it's a fairly common relay. So it was very easy to find the patterns.