When you're wiring in an aftermarket fuel gauge, there are four wires that you should first acquaint yourself with. There's the S Wire (fuel sender signal wire, connecting to the fuel pump), Positive Wire (connects to the wiring and fuses), Negative Wire (acts as a ground), and Gauge Light Wire (powers up any lights on the gauge itself). After you mount the gas gauge, you can start by wiring the Negative Wire to a metal surface on your vehicle for grounding. Once that's done, you can connect the Positive Wire to your car's fuse box. This may require using a test lamp to find the right power-carrying wire or fuse. Then, you can connect the S Wire to the fuel pump sending unit. Finally, you can wire in the Gauge Light Wire to the fuse that handles your dashboard lights.