"Pulsing" voltage, RPM drop with load.

Please do not confuse my results with OPs (JoePloe1) results, mine are only for comparison.

Did some testing on my 67 Dart w/273, stock 52 year old wiring, point ignition, key in the off position

Measurements at battery terminals, engine off, last started 1-2 weeks ago
Everything off 12.5V
Headlights on 12.1V
Brake lights on 12.2V
Brake lights and head lights on 12.0V

Measurements at Cigarette lighter , engine off, last started 1-2 weeks ago
Everything off 12.4V
Headlights on 11.5V
Brake lights on 12.0V
Brake lights and head lights on 11.1V

Measurements at Cigarette lighter , engine cranking, last started 1-2 weeks ago
Everything off engine cranking 10.6V
Everything off engine running at idle 14.3V
Engine running at idle headlights on 13.3
Engine running at idle brake lights on 13.9
Engine running at idle headlights and brake lights on 12.8