If it is only the rear lights, the problem has to be near the switch. I attached a portion of the wiring schematic and circled two wires. Each wire goes to a different signal on the rear of the vehicle. What I need you to do is check to see if there is power to both wires at the same time regardless if you select left or right. If you find that at the switch only one side at a time gets power, then we know the short is after the switch. If you get power from both sides of the switch,
Here is a link that you may find helpful:
Do this and let me know what you find.
Tuesday, December 8th, 2020 AT 4:33 PM