courtesy light wiring - ponton/heckflosse

[NutmegCT]

Wiring diagram shows courtesy light has two wires: one a "constant power" for when the light is switched on, the other providing power only when the door switch closes (when the door opens).

But the courtesy light unit has *three* wire terminals (three studs each with a screw to hold the wire).



Does anyone know how that courtesy light is supposed to be wired? There are only two wires inside the roof, and the unit gets its ground from the roof. What's the third terminal for?

And which wire goes to which terminal?

Thanks.
Tom
1960 190b