I swear to God this is true. Had a '61 Chevy with a 6 cylinder. 2 days after we bought it from the original owner ( who said he didn't want anything that wasn't a Ford in his driveway and since his son had left it in the driveway when he got married, he was selling it since it was still in his name ) we noticed that the battery was hooked up backwards---yes, backwards---negative to the starter and positive to the block.
When I first bought my '62 Impala, I got it home and shut it off. The generator light was faintly glowing was the reason and it was in the evening when it was getting dark is how I noticed it. Well it wouldn't start after I shut it off so I put the battery charger on it. The charger sparked like something was left on. Low and behold, the battery was installed backwards. Positive to ground and negative to starter. Luckily the battery was dead enough that it did not blow with the charger on it, but in the process I did fry some wiring.