Is it the alternator?

[johnpaulny]

I was stranded over the weekend and I'm pretty sure it's the alternator. Over the course of a long drive the battery power decreased to the point that lights were dangerously dim and even blinkers didn't work. Also noticed engine knocking on hard acceleration and hills. Car stalled when I pulled over. It's a new battery, so that's not it. Had it towed home and hooked up an external charger - started up and all power accessories worked and lights were bright. Disconnected charger and no accessories worked, lights dim, but car remained running.

Is this clearly the alternator?

Thanks in advance for advice.

[redbird1]

My first thought would be the battery.
Just because it is new does not mean it isn't defective.
Take it to a auto parts store and get it checked.
You should also take the alternator along and get it tested at the same time.
It is one or the other that is defective.
Bob.

[johnpaulny]

Thanks Bob. The reason I'm thinking the alternator is because the amp gauge pointed toward discharge when I put the lights on.

[redbird1]

Originally Posted by johnpaulny

Thanks Bob. The reason I'm thinking the alternator is because the amp gauge pointed toward discharge when I put the lights on.

A faulty battery would give the same reading.
Bob.

[johnpaulny]

Will definitely have them both checked out. The car is sitting in my garage for now - have to address it when I get back to my house. Thanks again.

[Ken in MN]

If the regulator is the original one, you might want to replace that, too. If the points inside are stuck open, the battery won't charge from the alternator. You can't really fix them and solid state ones are relatively cheap - lots cheaper than alternators.
Ken in MN