You don't say which car, but most have a slider switch. One position gives you a map l;ight, one shuts the dome light off completely and one psoition allows the dome light to come on when the doors are open. Is your switch set correctly?
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.