Where is the thermostat located on a 4.6 liter 2005 mustang?

The 2005 Mustang 4.6L doesn't have a thermostat in the traditional sense that you can easily access and replace like a home thermostat. The thermostat is integrated into the engine's housing. It's not a separate, easily visible component. You'll need to consult a repair manual specific to your vehicle's year and engine to find its exact location within the engine's coolant passages. You'll likely have to partially disassemble parts of the intake manifold and/or surrounding components to access and replace it.