1972 Plymouth scamp charging and grounding issue

1972Plymouth said
But it only happens when the lights are on, if they are off then its dead center. Could it be the lights causing resistance somewhere or is it something else? The battery is 12.68 when idling and 12.93 when brought up to 1700 rpm.

It's a common problem with these old girls, I can't tell ya how many I have owned over the last 40 years that do what you're describing.

I always started by checking all of the grounds, check the alt. belt to make sure it's adjusted up properly and not slipping under load.

From there it takes more looking into.