courtesy lights

[Trentaaa]

hey guys ive got a series 1 au falcon xr6 and just curious about the interior lights in the rear seats.....when i open my my door.....only one light turns on......the other light wont turn on when i open the door but it operates when i turn the switch?? may be a stupid question but i dunno but whats wrong??...is there an indidual relay or something for both of them i dunno hope u can help cheers