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Red light on beside voltage meter

Most cars have either an idiot light or a volt meter. This 1995 Buick Park Avenue has both in the same pod. The customer complains that the red light comes on intermittently, but the voltage continues to read just above 13 volts. Sometimes it’s dim or flickering, others it’s bright. It seems to be more prevalent when the headlights are off, rather than when it is under a heavier load with them or the A/C on. I have not had an opportunity to see the car. I’m hoping to get some ideas before she brings it to me. It has not failed to start.

So, what’s it trying to tell me?

Is the red light in question an alternator warning light? i.e. it turns on steady if the alternator completely conks out? Or is it for something else?

If it is an alternator warning light I suppose it is possible for a intermittent alternator to still combine forces w/a fully charged battery to produce 13 volts. Another idea, the volt meter is not accurate. If an alternator completely failed, the battery voltage would still be 12.6 to close to 13 volts immediately after the alternator failed. But that voltage would fairly quickly decline. But maybe the alternator’s fails for a short time, then starts working again.

My guess, I’m thinking this is a loose alternator belt.

The red light is definitely for the alternator. This has been going on of weeks, so apparently it is keeping the battery charged.

A loose belt, a tensioner that is not working properly, a poor connection at the battery, or a poor ground could all make this light flicker along with the possibility that the alternator may be on it’s way out.


The first thing you want to do is check the side mount terminals on the battery.

The positive terminal is notorious for corroding up and causing electrical problems.

So peel the red rubber cover off the positive terminals to expose them, so they be inspected for corrosion.