A Cross

So my taillights have decided to be difficult,they do not function at all when running lights would usually be on .brakes signals and reverse work fine, Ive changed out all rear light fuses , changed all bulbs , changed the junction that the two sides plug into, tried disconnecting the trailer plug , swapped out relay ( didn't make a difference) . One thing I've noticed is the sensor is sending accurate light readings to head lights and dash .. and even the reverse lights when its dark and the truck is exited. Im not totally clear on where to be looking for a ground issue as I dont see any grounds attached to the frame .. ... Plugs / sockets/ cables all look to be in good condition , another thing i noticed is that my license plate lights are out as well...any direction would be greatly appreciated