Power goes to +12v source, Load goes to the +12v lead on the device. Ground goes to ground. I assume it's a lighted switch or there'd be no reason for the ground lead. Is a 12v DC switch or a 125v AC switch. If it's an AC switch the light isn't going to work in it, however the switch will still do what it's supposed to. Install the switch on the power & ground leads coming from the vehicle.