Hi again. I found the reason for the exterior light problem.
The led bulbs I installed a few years ago in the licence plate lights, without problems until now, are both illuminating.
I decided to replace them with the original incandescent light bulbs and the exterior light warning went out.
I reinstalled the led bulbs and the exterior light warning came back on. Obviously a problem with the led bulbs even though they were illuminating and had been working without illuminating dash warning light.
I decided to try two new led bulbs the same type I originally installed. The new bulbs illuminated the same as the previous set of led bulbs but with no dash exterior light warning.
Must have been a problem with the original led bulbs after a few years use. Maybe the have a built in resistor or something that failed.