1965 Dodge Dart Charger

I checked all my 65 Darts and the cars produced after December 64 seems to have them. My brother in laws 65 Dart assembled in October of 64 has it too. I found one picture from American Rodder and that car had it. The wagon I bought from 37fleetwood in Los Angeles had never been touched and the plastic cover was there. I would guess that it was there so the kick-down linkage should get in contact with the positive cable in the relay.

But I checked the partsbook too and did not find it. Can it have been a assembly line part only? Or was it dealer installed when the car arrived to the dealer?