How were you testing the electrical connections? If you used a multimeter on the ohms setting it can fool you...a single strand of wire can give you continuity. If you put the meter on the dc voltage scale across the battery and watch the voltage drop it can tell you more. If the voltage drops off too far during cranking you may have a bad battery. If it stays up and the starter slows down you have a poor connection, broken conductor, bad relay or starter. The engine in your vid started and ran and sounded good. After multiple starts something was getting hot. Did you find the fault in the old harness?