My 78B’s courtesy didn’t work either when I first got the car. Turned out to be three different things.
1) The bulb had long since died and needed replacement. I always try the easy stuff first. /ubbthreads/images/graemlins/wink.gif
2) The courtesy lamps contacts had some corrosion on them. I pulled the entire assembly and gave it a good cleaning with some electronic contact cleaner (from Radio Shack) and a soft wire brush. Put it back in and the light would work fine when you manually turned it on.
3) But this courtesy lamp sill wouldn’t come on when the doors opened. Turned out that both door switches had some old paint & corrosion that wouldn’t allow a good contact. All I did was clean them up using some contact cleaner, along with some fine emery cloth and every thing was working great.
Also I had the same problem with the courtesy lamp in the truck (boot). Basically follow the same steps for the interior courtesy lamp. Actually – corroded contacts & burned out bulbs turned out to be a common scenario throughout the first few weekends I spent chasing down Lucas Electrical Gremlins.
/ubbthreads/images/graemlins/cheers.gif