The car starts fine in the morning. Since the battery has signs of leakage, I remove it in the afternoon, and put a new one, with a factory sticker indicating it was made two months ago.
There is no indication any power is coming in, not the lightest flicker of lights. I reinstall the old battery and see the same outcome. The circuit seems open.
The old battery gives a reading of 12.4V and the new one 12.5V. These are not loaded voltages, but I assume that for at least the old battery (which was used a few hours prior) there would be enough power for the lights, if not for the starter engine.
My first suspicion is that one of the cables is loose or broken. I had used a battery brush on both sides of the contacts, and so an electric interruption there is unlikely.
I can measure by an Ohm-meter to confirm that the ground (black) cable is fine to any point on the chassis.
What is a point of contact to determine whether the live (red) cable is fine?