1972 Plymouth scamp charging and grounding issue
This is true but it "gets worse."
It is common for the backyard rebuilders to MODIFY the older cases and add a brush, and it is somewhat common for the 'proper' alternator to have hardware or defective hardware which INCORRECTLY causes one brush to be grounded.
The short answer is "you need a squareback" alternator, AND you need to electrically check that neither brush (field) is grounded to the case
Below is an improper 69 / earlier case which HAD been modified by a rebuilder to install an insulated brush at 12 o'clock. This "converts" the unit into a 70 / later unit. One problem with this is that the brushes used don't fit properly, and the second is that someone can install a grounding (original) brush which won't be good in a 70 / later installation
Below is an interesting situation. On the left is a roundback, I've never seen one. This appears to be factory, and appears to accept EITHER a grounded or insulated brush. The one YOU WANT is on the right, a "squareback". These are superior in design, put out better at low RPM, and "only come" in isolated brush, "what you need."
This is true but it "gets worse."
It is common for the backyard rebuilders to MODIFY the older cases and add a brush, and it is somewhat common for the 'proper' alternator to have hardware or defective hardware which INCORRECTLY causes one brush to be grounded.
The short answer is "you need a squareback" alternator, AND you need to electrically check that neither brush (field) is grounded to the case
Below is an improper 69 / earlier case which HAD been modified by a rebuilder to install an insulated brush at 12 o'clock. This "converts" the unit into a 70 / later unit. One problem with this is that the brushes used don't fit properly, and the second is that someone can install a grounding (original) brush which won't be good in a 70 / later installation
Below is an interesting situation. On the left is a roundback, I've never seen one. This appears to be factory, and appears to accept EITHER a grounded or insulated brush. The one YOU WANT is on the right, a "squareback". These are superior in design, put out better at low RPM, and "only come" in isolated brush, "what you need."