Hi, everyone. I've got a 1991 Chevy Camaro Z28 with 350 TPI. The volt gauge needle fluctuates whenever I apply the brake, activate turn signals, when the cooling fan kicks on, and using the power windows. I've done a search and didn't find anything. I had the alternator tested at Autozone and they used the rolling machine and put a load on it and showed it stayed at 12.4 volts at the battery but my gauge fluctuated to 8 volts and stayed there for quite a while until the load was taken off. The battery was also tested and passed. I went to Kragen for a second opinion and they used a hand held tool and told me to on the A/C to put a load on the alternator and passed the voltage test. The battery was also tested and registered at 12 volts at full load. A month later, I took the alternator off and had it bench-tested at Kragen where the alt. was purchased originally. It passed their voltage load test. It registered at 12.5 volts at full load. He told me to replace the serpentine fan belt and the tensioner. I put on a new belt and no change, the needle still fluctuates. The tensioner is fine-I see no vibration at all. Any ideas? Your help would be greatly appreciated.

 

Factory gauges are not exactly famous for their accuracy. They're meant for getting across a rough idea of the state of their function. You can add an aftermarket voltage gauge if you really need to know an accurate voltage. But there's not really much you can do about the in-dash gauge.

 

So, the alternator is not the culprit. Well, does someone recalibrate these gauge clusters? How much do they charge? How do I check for the accuracy on the voltometer gauge?