High Charging Rate. Found Voltage Drop Need Guidance Please

I am guessing for tests when ignition in run, motor is not running. Test with engine running, should give about 13.8 V at IGN terminal, same at ballast high side. The 12.4 - 11.6 = 0.8 V undesired drop, so battery voltage 13.8 + 0.8 = 14.6 or more, since drop increases with other loads.

Perhaps others can suggests fixing drops on a 65.