Larry, good news, the courtesy lights are still in production, here with switch at Alfastop - http://www.alfastop.co.uk/cgi-...p;search_text2=light Alfa part #1493.80.716 for Giulia 101.... or Lancia Fulvia https://www.pieces-fulvia.com/...ulvia-all-models.htm
The dimmer is a wire-wound variable resistor, google LUCAS Rheostat Dimmer Switch , Lucas part 78455A or 78418... It likely won't do anything if you have LEDs, and if you don't have LEDs you probably don't need a dimmer ...So populating with a simple on/off switch is not a terrible idea. One of my long-term-will-probably-never-do-projects is to make an LED driver that uses the original rheostat...but I am so far from needing optimum lighting for night driving to distinguish whether I'm driving 45 or 50 mph...on a 200mph speedo
Lee