1985 coupe deville computer going?

[nycjohn]

I have a 1985 cadillac coupe deville. Recently when I started it up I noticed that the electronic gas gauge read that I was on “E.” I knew I had about 7 or 8 gallons in tank. I drove it around, and slowly the fuel started rising. I went to gas station and filled tank. It read “F” then quickly went to 15 gallons. (I believe it holds 18) Anyway, next morning I started car and since it was chilly, I adjusted temperature. Suddenly all lights on dash board came on/stayed on. Battery light, service light maintenance required, etc. Car then went dead. Restarted OK. I just ran the car for about 10 mins. all seems fine. Do think computer system is wigging out? Tune-up required, alternator going?
This is not my primary car. And since its almost 20 yrs old. I don't want to waste time and money. And certainly don't want car to just decide to shut down next time out. Any ideas?

[MarkC]

Bad alternators and batteries make the electronics do weird things. Try testing the battery voltage with a volt meter while the car is off and running.