Where is the fuel cut off switch on a 2003 chevy truck?

There's no single, universally located "fuel cutoff switch" on a 2003 Chevy truck like you might find on some machinery or boats. The fuel system is controlled electronically. To stop the fuel supply, you'd need to either:

* Turn off the ignition: This is the primary method. Turning the key to the "off" position interrupts the power to the fuel pump and injectors.

* Disable the fuel pump relay (potentially): This is more involved and requires some mechanical knowledge. You'd need to locate the fuel pump relay in the fuse box (under the hood or inside the cab, depending on your truck's configuration) and remove it. However, this is NOT recommended unless you know exactly what you're doing, as it can be dangerous if done incorrectly.

In short: Turning the key off is the correct and safe way to stop fuel flow. Don't attempt to fiddle with relays unless you are experienced with automotive electrical systems.