hi there, using a voltmeter logger i have taken voltage measurements from both the cig lighter and the accessory socket. for a kia they give 12.1-12.
5v when engine is on or off. while engine is running if you turn on headla mps or fan etc, momentarily it will spike up to 13.8 and then go back to 12 .5. i guess the alternator might be a smart type which disengages with a cl utch if not needed.on other cars i tested this on ( e.g. ford, peugeot) i found that with car engine is off you get 12.5, with car on you get a steady 14-14.1v , regard less of if you turn on headlamps etc.
i suspect that certain electronic accessories meant for plugging into the cig outlet might expect 14v if they are intended to work with engine runnin g, and might not work as intended with the pure 12v. i am finding this issu e with a navigator which has a internal 12v battery which is charged from t he accessory socket.
anyone else observe this? thanks K