my 78 wagon's "chg" idiot light stays on. the alt looks new or rebuilt. any thoughts, diagnosis, hints? anyone know how long the wagon will drive on a fully charged battery if the alt is truly shot?

Just because the alt looks good doesn't mean it is. Have it bench tested at a shop.

 

On a battery you will notice 3 numbers... Cold Cranking Amps, Cranking Amps, and Reserve Capacity. The reserve capacity is the number, in minutes, that your battery should last with a bad alternator and minimal accessories. That is, if the battery is fully charged when the alternator dies.

 

So... a battery with a reserve capacity of 60 should last 60 minutes with no accessories running- by the book.

 

Don't bet the farm on it though.

 

If I knew my alt was dead, I would only drive the car in order to get it to the quickest safe place before it totally died. Whether it be home, a friends house, an auto parts store, or in the case of my last alt failure- a church.

if I parked my red Camaro at a church, it would be burned to the ground in a matter of minutes......thats what happens when you have a license plate like mine WKJ666....we killed Jesus 666......and its not a vanity plate either:eek:

 

it sounds like either your alternator is bad or possibly you could have a bad battery cabl;e or wire so it is not charging the battery all the way