Replaced battery and alternator but battery light still coems on until you hit gas ten battery light goes out

Steve Allison

• 5569 Answers
• Posted on Oct 03, 2008

SOURCE: 2002 sonata 2.4l battery dash light on. replaced alternator. Still not charging

I don't know if your car has an integrated regulator or not; some house the regulator in a section of the alternator case, others mount it remote from it. The regulator monitors the load and battery voltag,e primitively but effectively, and controls the current flowing through the field winding of the alternator to ground, changing the magnetic field intensity and consequently the voltage output of the alternator. The 'hot' end of the field is internally connected to the + output, the 'cold' end is controlled by a transistor inside the regulator which, in turn, is controlled by circuitry monitoring the system voltage.     Some alternators can be tested by sticking a wire through a specified opening, actually shorting the controlled end of the field to ground briefly, while monitoring the voltage across the battery, doing this though for seconds only. This essentially bypasses a suspected defective regulator; this causes the output voltage to rise instantly to its maximum of ~17 volts if the alternator is OK.
I don't recommend poking a wire at random into an available opening so having a service manual (Haynes-Chilton) would be nearly mandatory.