License Plate light help???

Hi i need help with my problem solving as far as what is wrong please help. My license plate light
works when i open the trunk but will not work when lights are on and driving. The dash says license plate light not sure if that is a indecator or what but i checked the conection and that is fine as well as the fuses and that also is fine please help me troubleshoot before i get pulled over.. Thank you for your time as allways confused and petrified Tom...