Easiest way to see if it was factory installed is to have the parts guys at any Ford dealer pull up the Historical Vehicle Bill of Materials (HVBoM). Otherwise, there will be a standard 110V plug under the hood near the front, and wiring coming out of a freeze plug. You’ll just have to look.
Here’s a shot of the aluminum block in my ‘03 Cobra (custom build): you can see the block heater and cord coming out of where a freeze plug would be...
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The plug right up front where it needs to be easily accessible - same idea for any vehicle.
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