While driving at night. Dash lights gauges radio climate control all turned off. Stayed out for a few seconds they came back on. Process repeats every minute or so. Engine still runs and head lights stay on. Just everything else keeps going out. Charging light came on and the check engine light came on. Next morning Battery was dead. I charged the battery and ran a voltage test at the batter with the engine running. 18 volts at a idle. The code came back for as high voltage output. Any idea what would make the alternator put out that high of voltage?