[stellar]

Originally Posted by Sirrotica

Disconnecting the alternator while the car is running it a very good way to ruin a functioning alternator, seen it done back in 1970 on a Jeep. It ruined the alternator. It doesn't always blow the diodes out, but it certainly can. This was a Prestolite alternator, and it was functioning before the hack mechanic pulled the cable off. The dealership had to eat the repair, because the Jeep came in for a tune up, the charging light wasn't on, until the guy pulled the battery cable off while the engine was idling, trying to show off how he tested alternators without any instruments.

A much safer field test is to use a thin piece of steel like a hacksaw blade, and place it at the bearing end of the stator shaft. If there is a magnetic pull, the alternator is charging, if no pull then it's not. No chance of ruining a perfectly good alternator by blowing the diodes.

Please heed Sirrotica's advise. Very good advise for a quick charge-no charge test when out in the field that will not cause damage. A battery disconnect while running may damage not only the alternator, but also other electronic components are at risk of damage. The disconnect test is a throw back from the pre electronic days when generators were used. In 1970 jeep used an electronic regulator and it was probably damaged by the battery disconnect, causing the charge light to come on.. Ignition modules were also know to be damaged by this test. No not disconnect the battery when the car is running.

[kenelder]

Having owned a ‘71 Formula 400 from new until I sold it with well over 100k miles on it, I’d like to offer a thought. Mine had a similar issue one time and eventually I found it after the shift cable froze up in D. In my case the chassis ground wire in the engine compartment fell off. It’s a braided strap at the back of the engine that has a push on connector screwed to the firewall.

When that ground falls off, then the panel grounds back to the engine through the trans shift cable. In my case the current in the cable on a long drive got the cable hot enough to melt the plastic housing to the cable thus freezing it in place.

Maybe you shod check the chassis ground along with any other grounds in the system…..

[lust4speed]

Seems like another test with pulling the battery cable off is if the battery blows up from gassing while it is charging and cable is pulled off creating a spark. You then know your alternator is working. It also allows you to purchase a new battery after being released from the E.R.

[Dynoking]

As others have said the alternator is not the likely cause of your problem. And definitely do not disconnect the battery terminals while the vehicle is running! Google voltage drop testing starting systems. This test is easier than it sounds and will help you find compromised wiring and connections in your 50+ YO vehicle. T Be sure and perform the tests while the symptoms are actually occurring.

[Ramairnacho]

Ok I apologize for mentioning removing cable I done it since a boy on old cars another easy way is just testing voltage with ohms meter at battery if volt continue to drop remove take to local auto store to rest if it reads more than 12 volts and is stable its agood alternator. I. Not trying to have anyone hurt. Harbor frieght oh.s Meyer under $10.

[Sirrotica]

Originally Posted by lust4speed

Seems like another test with pulling the battery cable off is if the battery blows up from gassing while it is charging and cable is pulled off creating a spark. You then know your alternator is working. It also allows you to purchase a new battery after being released from the E.R.

Most people don't believe that all it takes to blow up a battery is a tiny spark. I blew one up that had just came of of a trickle charger when I was 15 YO, just hooking up jumper cables to it. My father was a mechanic most of his adult life, he warned me about how easily it is to blow up a battery, but he was my old man, and at 15 YO I was much smarter than he was.......LMAO Many years later I told both of my parents that, the older I got, the smarter they were...........

Later in life, we had a wintertime no start car that I hauled in with my wrecker. The battery was of course dead, it was on the charger but didn't seem to be charging. I twisted one of the battery clamps to make sure it had a good connection, while it was charging and boom, I exploded my second battery.

A friend of mine that owned a body shop blew one up , and got a fragment in his eye. Fortunately the fragment was retrieved, and he did not lose the sight in his eye.

Hydrogen gas makes a very good explosive.......