QuestionLast week I replaced both the battery and alternator in my 1994 Geo Prizm LSI (Corolla), 1.8 liter, 5 spd. Car has nearly 300K miles and, although I was not having electrical system problems, I previously had to replace two alternators at the 100K mark and the battery was about 5 years old, so I figured I’d get a jump on the winter with new alt and battery. New battery is a Diehard Gold and alternator is the premium Delco unit from NAPA with lifetime warrantee.
The morning after I installed the new battery and alt, my charging system light (the little battery icon) began coming on intermittently. It was not coming on at all before the swap. I double checked the wiring at the alternator and all was secure. The light appears with no fixed pattern. Sometimes it comes on at idle and goes off when I rev, and sometime is goes on at higher rpms and goes off when the engine drops to idle. Sometimes I’m driving down the freeway and it just comes on and stays on for a few minutes and then goes off. Sometimes it flickers and sometime its steady and sometimes it seems to be flashing at a fixed interval.
I threw a charging system tester on the battery while engine was at idle and it indicated failure, showing a high voltage at the battery (slightly over 16 volts). It would appear that maybe my brand new premium alternator has a bad voltage regulator? Could this also be caused by a bad ground somewhere?
Is the voltage regulator on these Delcos replaceable as a separate part? I know I could get a new alternator but if it’s quicker and cheaper to just replace the regulator, I would rather do that.
If the alternator is really overcharging, why isn’t the charging system light on all the time? Thanks for your insight.
AnswerSince the alternator has a lifetime warranty I would take it back and get a new one, most autoparts stores can check the alternator output and if it's overcharging then the regulator or another component is malfunctioning, the regulator is not replaceable seperately.
