As I was troubleshooting the boards to locate the problem with my curb lights, everything seemed to be working on the boards, and I had no blown fuses. My next step was to swing out the ECC and look at the rear of the motherboard as Truk had recommended.
Unfortunately, I realized that the sliding Joey Bed prevents the motherboard from swinging out, so that was a definite roadblock. Since it looks like a significant chore to remove the Joey Bed, I may at least temporarily tolerate not having the left bank of curb lights.