To find it:
1. Consult your owner's manual: This is the best place to start. It should have a wiring diagram showing the block heater circuit and the location of any protective devices.
2. Inspect the wiring: Trace the wiring harness from the block heater itself. Look for an in-line fuse or a circuit breaker near the engine. These are often cylindrical and may have a visible number or rating stamped on them.
3. Check near the battery: Sometimes, the protection device is located near the battery, but this is less common than being near the heater itself.
If you can't find it yourself, a Ford dealership service technician will be able to locate and identify the protective device for your block heater.