[Oldsguy]

I checked my wiring diagram now that I am home. The grey (actually, it was originally white according to the drawing but I agree, it looks grey) wire from the lamp should be joined electrically to the switch which has only that one wire to it, the other side of the switch is shown as ground which means it is mounted in metal, grounded to the chassis, to the battery that way. It works the same way as the door jamb switches do (and is in fact in parrallel with them so that any one of them should activate the map light as well as the courtesy lights). Don't see where it is activated by the main headlamp/dimmer switch though. The orange wire is always hot, as are the other orange wires to the other lamps.