Here's a strange situation I encountered last night that I'm trying to wrap my head around.
My mother in law drives a 2011 Subaru Legacy. Last night, her battery (since replaced) died -- not totally dead, but no longer had enough power to fire the starter.
I brought my wife's car, a 2018 Chevy Traverse, to provide a jump. I made the negative connection on the provided ground post rather than to the battery. When I made the final connection, the entire electrical system on the Legacy went dark -- lights, accessories, everything. As soon as I disconnected the jumper cables, everything came back. During this time, the battery voltage reading on the Traverse was reading around 14 volts.
Unable to successfully jump, I swapped cars and brought my car, a 2006 Kia Spectra, and repeated the process. Everything worked as it should.
My question is this: what was going on that the jumper cables from the Traverse made the Legacy go completely dead? And what was different that it didn't happen when I used the Spectra? The polarity was correct, both cars work properly, no fuses were blown. I'm at a loss to figure out what happened.