1966 Valiant Engine wiring harness

I just thought of something. With the headlights on, the tail lights are also on. (The front parking lights may also be on but most '66 models turned them off when the headlights turned.) So that may explain the 4 - 5 Volts.
The big IF is if the battery was fully charged and supplying power at roughly 12 Volts. But for now I'm assuming thats the situation.