Questions and Answers

Charging System Mystery Q. The alternator gauge would suddenly drop below 10 volts and the idiot light would come on, so I figured bad alternator, which I replaced. While I was at it I also thought that it was time to change the battery, so I did. Well after that, it was fine for a short time then the problem returned, I found if I revved up the engine the problem would go away.

A load charging system test indicated a faulty diode pattern in the alternator, after the problem reappeared and revving the engine did nothing. The alternator had a lifetime warranty (not rebuilt, all new) so I replaced it again.

Now it seems fine, however yesterday suddenly the gauge dropped again and the idiot light came on and went away. Could it be another defective alternator, or is something else causing the problem?

My hunch is a faulty starter solenoid could be causing a short to the charging system.

I am at a loss as to what to do next? Occasionally the car will not start but I am attributing that to the park ignition interlock, because if I put the car in neutral it starts right up. Could it be a faulty solenoid causing the charging system problem. How could I identify the problem?

1989 Pontiac Grand Prix SE
2.8 liter engine
Power Steering, Brakes
Auto Transmission
Fuel Injection, AC, Cruise Control
Mileage: 100,200 (I know, it is a good station car)

What are you thoughts?
Thanks in advance.

A. It's not unheard of to get a string of bad parts, however I don't think that is the case here. You can try another alternator from a completely different source to see if it works any better than the ones you've been getting.

Most often this kind of problem is caused by a fuse or fusible link that is burned out. At this point I would suggest checking all the fuses and fusible link with a test light or DVOM and make sure they are all good.

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