Cadillac Repair: engine light and charge light problem for Cadillac Deville 1990, e 85 gasoline, autozone

Question
Cadillac Deville 1990, 4.5 liters
I bought a battery from AutoZone and I told the guy that I wanted to sell my car and I needed a battery just to get it started. I think he gave me one that was too small and not enough voltage. I have had many different problems with my car. The problems are as follows: AC/Heater never completely turns off; a slight breeze of air can still be felt. Battery  light randomly comes on and off for about 6 hour durations; sometimes staying on, sometimes it flickers, very random. Except when I am speeding or accelerating the light turns on instantly and lights very bright. Also it dims out when more power is being used and the light gets brighter when you press on the gas. It also synchronizes with the bass that I have installed in my vehicle. When I turn my AC on to "auto" it begins to make a noise; sort of like a compressor but does not sound normal or ordinary. After driving around with the AC on for about half an hour the "service engine soon" light comes on. The motor feels like its stuttering a bit. Also, I have recently been experimenting with E-85 gasoline. I filled the tank 10 gallons with E-85 and 6 gallons with  regular unleaded 87. NOTE: This is the first time I have done this. P.S. Before, I used to put water in the radiator instead of anti-freeze. i want to fix this car myself so please dont make any suggestions about taking it to the shop to get it check out or anything similar to that.

Answer
AC/Heater never completely turns off; a slight breeze of air can still be felt. THIS IS NORMAL.

Battery light is caused by a faulty diode in the alternator.

I would have to hear this possible compressor noise.


As to the service engine soon light you have to retrieve the codes from the computer.