I was sitting in evening rush hour tonight and suddenly my volts go from 14 to 10.5 and my lights dim. It stays at 10.5 and besides the lights dimming there is no other change, like rough idle or noises or anything. The volts do not increase with RPM as usual and I turned my lights off to test and there was also no change. About 15 minutes later it jumped back up to 14 for about 2 minutes then back down again. When I got home I couldn't spot any visual problems under the hood. My alt's 1 month old and my battery is about 5 years old. I have a 92 305 tbi. The volts didn't really drop and raise suddenly, it was more like a 3 second slide. What kinds of things could be causing this? Thanks.

A one-month old alternator.

Was it really "new"?

You caught me. An Autozone rebuilt cheapo. But the last one lasted me 5 years. Are you suggesting that this could be an alternator problem?

Strongly. I usually go through two or three before finding the 5-year one. One created a nice bonfire under the hood of the wife's Bonneville. The fire department enjoyed the exercise.

I guess I'll bring my tools to Autozone and let them check that and the battery. Would the alternator definitely fail their tests if it's an intermitant problem? Thanks for your help.