I'd need to see a wiring diagram. 96-7 cars used wires to the rear lights but 98 ish and up used CAN bus for many functions. I don't know if there is a CAN module for rear lights on 98 +.

CAN dramatically reduces the amount of wiring in a car. As an example, each door has a CAN module to run the glass / locks / alarm / side view mirrors / lighting / power seat switch. Run 2 wires for CAN communication , power and ground then everything works by sending a message rather than having a wire for each function.

Furthermore, wiring shrinks in count and gauge at the window and other switches. The power window switch now has 2 wires for CAN, power and ground.

I've had various electronic modules develop a sensitivity to high / low voltage resulting in various odd behaviors.