TAIL LIGHTS

MY TAIL LIGHTS DO NOT WORK, I HAVE BRAKE AND TURN SIGNAL LIGHTS, HEADLIGHTS AND HAZARD LIGHTS WORK. THE FUSE IS IN GOOD CONDITION, THE RELAYS IN THE TRUNK AREA HAVE ALL BEEN REPLACED WITH NEW, THE REASON FOR THAT IS I DONT KNOW WHAT RELAY IS FOR WHAT AS THERE IS NO RELAY BOX COVER. I DO KNOW THAT IAM NOT GETTING POWER TO THE FUSE IN THE TRUNK,FOR THE TAIL LIGHTS. THIS IS DRIVING ME NUTS, CAN YOU HELP ME OUT ?
THANK YOU