After almost 3 years of TR ownership, I just now discovered this hiding in the frunk. One question: where does it plug into? The extruding tip makes it non-applicable for the cigarette lighter receptacle (I tried on another car).
In the "electric socket" inside the glovebox on the RH side -- see Section 2 in the TR OM Glove box compartment. (That style plug and socket is a quasi-standardized thing -- used on BMW motorcycles too, IIRC.)