2000 Ford F-150 acts like battery is dead, won't start

My truck has had the gauges pegging maximum for a while now when I turn the ignition to on. It always started though. The other day while driving, the radio went off then the wipers. Both came back on at different times and then the radio continued to go off and on routinely for the next few days. The next day the trucks key reminder ding dinged as if the keys were in the ignition when they were not and the radio came on by itself while parked with no keys. I cleaned the battery terminals as they were corroded and I thought it might help. The alarm chirped when I reinstalled the cables. No big deal. Then when I went to start it again the radio would not come on, the gauges pegged maximum and one of the relays under the dash kept clicking. The radio would come on when I turned the igniton to accessory but nothing else would light up. Then the alarm went off and would not respond to either remote so I disconnected the battery to get it to shut off. Now it just acts like the battery is dead when there is actually 12.43 volts present. The relay continues to click under the dash and the truck still wont start.