1991 Eagle Premier Low visibility on dashboard instruments.

This involves the trip monitor (right side) and the
service monitor (left side) of the instrumnt panel.
All of the usual instruments work properly.
These two items plus the temperature control light are not bright enough to read. They are not controlled by the dimming switch. I know that the units are working because they can be read when the proper lighting (sun or flashlight) hits them at the necessary angle. How can this be corrected?