Perfect amount of detail in the video, also the only one on RU-vid in English. I saved a couple of hundred bucks following you on your belt changing journey
when you were putting the new alternator from underneath you shorted the alternator against the connecting wire since you did not also disconnect the positive terminal from battery.
Electrical power requires a positive AND negative path to flow electricity. There is no short because with the negative of the battery disconnected, there is no electrical path even if he touched the positive lead directly to ground.
