Hope you find the culprit causing your delima. One of the best (and safest) ways to check-out all rear facing lights is back-up to a big picture window at a shopping center. Look in your rear view mirror(s) and check the "reflection" in the big window. You can confirm every light (L&R turn signals, brake lights, running lights, back-up lights, 3rd Brake light), all at one time and even in bad weather without ever getting out of the vehicle. This simple method eliminates the need for a second person to seperately observe.![]()