To find it, you'll need to specify the engine type (e.g., 5.2L V8, 5.9L V8, Cummins 6BT diesel). Once you provide that information, I can give you a more precise location.
Generally, though, you should look in the vicinity of the fuel tank and/or along the frame rail near the fuel lines. It's often a cylindrical canister and may be mounted vertically or horizontally.
