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Jim Grant's Tech Tips
'89 VW Jetta GL, Battery Light Problems
Q:
I am the frustrated owner of an‘89 Jetta GL that has been giving
me fits lately. My wife noticed the battery light was on one day. On her
way home from work the car died. It appeared to be a bad alternator. I
put in a new alternator, the battery light remained on, but all my multimeter
probing said that the battery was taking a charge. Two days later it died
again while I was driving it. I put in another new alternator (traded
AutoZone for another one) thinking the refurbished one was bad and I put
in a new battery. Again, all signs said that everything was OK, but the
battery light was still on. I talked to a knowledgeable person about it
and he looked at the car for me. He said that the light shouldn't be on
that everything was OK. I let the car sit for a week and the battery was
dead. Obviously, something is pulling current, when the car is off. Do
you have any ideas?
A:
After changing the battery and the alternator twice you can say with confidence,
they ain’t broke. With a battery warning light remaining on you know
something has to be amuck electrically. On most vehicles today when you
turn the ignition switch on, electrical power is sent to the battery light
and from the battery light to the regulator that controls the alternator.
This little electrical signal is the cue to the regulator the engine is
going to be running any minute now. The job of the regulator is to control
how much electricity the alternator produces. Once the engine is running
and the alternator is producing enough electricity the regulator will
cause the battery warning light to go out. If the light is not going out
then the alternator is not charging, the regulator is bad, the wire to
the regulator from the battery light is not plugged into the correct connector
or the electrical signal from the battery warning light is going somewhere
else. So, with all of this in mind, I think it would be best if you took
your vehicle to a technician that can check/diagnose your battery warning
light and possible charging system problems. Once you have the answer
you can replace the part that will keep your wife’s vehicle going.
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