no tail lights but have reverse lights and it's not the bulbs?!

My Yukon has no running lights in the back but has reverse on both driver's and passenger's sides. There is brake lights on passengers side and across the top but not on driver's side. it also has turn signals on the passenger side but not drivers. we checked the bulbs and that's not it and we even plugged the whole light assembly from the passengers side into the drivers side and still nothing. Not sure why it has power for the reverse but nothing else is working on the driver's side.