GRJ, I think I may have the same meters as you do in my voltage car. They too work off just one power supply, just as yours do in your car, FWIW.
TedW, I had a couple of these meters go dark as well! Fortunately they are pretty inexpensive, and then GRJ helped me out with the isolated DC to DC converters. That was a few years ago and all has been well since.