I was getting 18 volts to the battery two weeks ago, The headlights were bright for a change. I changed the regulator. The battery, alternator, and voltage regulator are new. I'm only getting 12 volts to the battery and the truck doesn't idle unless I keep the RPM's at about 2,000. Although the battery isn't getting the 13.9 volt that it should be getting, it is being charged enough to keep the truck running, even with the headlights on. Any help would be appreciated.

 

I would double check the alt. out put .. new dosent necessarly mean "good" .. I have seen many , many, new alts off the shelf be duds .