The trunk light on my 230SL (#018381, Oct. 1966) operates only when headlights are on. I think this is true for all W113 models.
Rodd
Powell, Ohio, USA
1966 230SL: arabian gray, natural leather, euro, auto, both tops
1994 E420: pearl black, black leather, auto (FOR SALE)
2006 C230: alabaster white, 6-speed manual, no options