Had the battery/generator light come on. Check battery, had voltage but couldn't take a load, I replaced it. When the engine is cold the alternator will put out 14.2 volts. Once the engine has warmed up, if you shut it off and restart it, no output from the alternator only battery voltage. I checked this at the back of the alternator to make sure this wasn't a grounding or started Y cable issue. I noticed that if I unplug the exciter wire, I get 14.2 volts regardless of the engine state, cold or hot. I checked the voltage at the exciter wire and was receiving 12v when the engine was running. If I plug the exciter wire back up with the engine running and the alternator providing 14.2 volts, I see no change until I restart the vehicle. Once I do that, I'm back to no alternator output, until I disconnect the exciter wire. I'm trying to determine if I need to replace the alternator or if I may have a larger issue looming.
It is a 2006 Cayenne S.