All other lights work turn signals,brake lights and head lights. I have checked the bulbs,grounds,fuses,and the boards. please help!!!!!!!

its only one wire going to both rear lights. Do you have dash lights? if so remove one light bulb and check for power and ground. if missing power then its an open in the wire going up to the front. If you have both power and ground recheck ground with the lights on and the bulbs in you should still show a ground if it shows voltage then the ground is week and the boards or the ground conections may be bad. check the plugs to the boards also. Do you have front parking lights? If no parking, dash or tail lights you have a bad switch or no power to it