Map light switch

1971 dart, bone stock, map light only works if dome light is on (door open or headlight knob turned all the way to the left). Never touched the wiring
friend's 1970 duster did the exact same thing, at first I thought mine was wrong, but his functioned the same way.
the only thing the switch does is turn the map light off completely, or on only when the dome light is on

there must be more to this, would be interesting to hear from others