I have a 78Z. When I am at idle my charge light comes on and the volt meter is at about 13. When I drive and keep the RPM,s up around 2500 it goes off. If I turn on my parking lights it will come back on until I get up to 3000rpm. When I turn on the lights it wont turn off, even if I hit 5000 RPM.
My question is do you thing it is the alternator or a wiring issue. This just started happening today. I check the belt and re-tightened it.

Any ideas or thoughts will be welcomed.

Thanks.

 

Yes, sounds like your alternator is bad. Check your battery cables too.

 

I installed a later model GM alternator. It is internally regulated and therefore there is no fuss with the external regulator. It was a fairly straightforward instal, but did require some fabrication for mounts and tensioners. This thing is 100 amps too, big upgrade to the stock Z alternator.
-jeremy-

 

Yes, sounds like the alternator, but... I had a similar problem and took the alternator to Autozone and it passed all of their tests. After several hours of looking for bad connections, it turned out to be a flaky fuse that measured 16ohms across it. so, a new fuse fixed the charge indicator.

Free testing at the auto parts store is great for finding or ruling out alternator or battery problems.

 

Its not the alternator. it is either the battery or a ground issue. i have tested the alternator completely. i am testing the battery now.