1997 Jeep Laredo altenator battery or a ground?

Well I put a new radio in my grand cherokee and initially I had an extra mute wire on my new wiring harness and an extra wire from the factory with a female connector that slid on a metal tab sticking out from the back casing of the factory radio so naively put them together but after seeing how my voltmeter reacted when I would turn venting on I came to the conclusion it was a ground that appeared to be for controls around the radio, but since that with my vehicle off and having the radio on for 5 mins or so the voltmeter would go down the the warning underline and just drop all the way down and activate a check gauges alarm, so I changed that but now it is going from 14 volts when running to acting like its drained within 2 minutes of being shut off it will normally still crank and ive been told to check my alternator but would like some different input because ive charged my battery on a charger and it pretty much just does the same thing but a lil more length, tho I do find the notion of a regulator in the alternator being bad plausible but would like a better idea before I take it out, another thing I did that was dumb was turned the battery charger up to 30 amps which I didnt realize could potentially damage things but I do remember some odd noises when I turned the key with that on