My Calif. 83 300D turbo also had the factory installed cellular phone. OKIE if I remember correctly. The antenna cable ran from the inside rear window connector around the inside top of the window gasket and down to the control (?) box under the rear pass. seat on the right side. From there the wires led to the trans hump and to the handset/cradle in the center console.

I think that most if not all 83's had "factory" installed cell phones installed.

Wayne