Where is the thermostat on a 1996 4.9 liter ford f150?

The 1996 Ford F-150 with a 4.9L engine doesn't have a thermostat in the traditional sense that you might be thinking of (like a dial you adjust in the cabin). The thermostat is a temperature-regulating valve located in the engine itself, within the engine coolant housing. You'll need to access it by removing parts of the engine compartment. It's not something easily visible or accessible without some mechanical knowledge and tools.