Hey guys I have a 2002 Z28 auto that i don't drive but a couple times a month. The other day I drove it everything seemed fine then when it got dark and i put the headlights on the voltage gauge was reading really high and the headlights and the dash lights were dimming and brightening. The car starts fine.

Thanks

 

It was reading really high or low? What does it read during the day with nothing on? You need to check what it's really reading, hook up a meter to the batter while the car is running to see what you're actually getting, don't rely on the factory gauges too much.

 

Sounds like a bad ground, check both ends of the negative battery cable.

 

Thanks for the reply guys. Today I tested the alternator with A/C, lights, radio on I the volt meter was reading 14.5v so i tested with everything off and still 14.5v. Checked the grounds and they are tight. Guess I will just have to drive it around again and wait for it to happen and then check it. Hard to tell if the lights are dimming during the day, may go for a ride tonight and see what happens.

 

voltage reading doesn't tell the whole story about whether an alt if functioning properly. You need to have a machine hooked up to put a load on the system at rpm (usually around 2000-2500); and it needs to read the amps + waveform of the output and test the diode pattern.

If your getting voltage fluctuations, have the battery AND alt tested at a shop. One of the cheaper places to do this is Sears, they only get 15 bucks for the tests. Dealer's around here charge 1/2 hr plus at flat rate for this. ($50+).

Could even still be the battery if it starts fine (small chance, but worth checking). Or possibly the belt is slipping a little.

 

Carquest can also check the charging system, while still in the vehicle... They use OTC Sabre HP diagnostic tester... Sound like the internal regulator might have an issue..