A wandering mind and diminishingly relevant questions

So I had my portable power source out to get the cord I use to charge my phone when a question popped up unbidden in my mind. When using jumper cables you generally hook up negative to negative and positive to positive because for 99% of cars on the road that’s what works. Then my questionably inquiring mind wanted to know (because I don’t know), what if you’re charging an older Ford? Back in the day they used positive ground instead of negative ground. So, would you hook up neg./neg. and pos./pos. or hot/hot and ground/ground? Then I remembered back in the day most electrical systems were 6 volt instead of 12 volt like most are now. Can you safely charge a 6 v. system from a 12 v. source? Then my mind really wandered: any issues with charging a car that has a generator instead of an alternator? Does any of this really matter? Would it help if I hooked up battery cables to my ears to generate some electrical activity in my brain?

On a positive ground car you hook up negative to the negative post first then the positive lead to the positive post.
It is extremely risky to jump a 6 volt system with 12 volts, it is possible for the 6 volt battery to explode, not to mention the possibility of causing damage to the 6 volt vehicles electrical components.

There was a series in either Popular Mechanics or Popular Science magazine In the 50s and 60s called (I think) Gus’ Garage which covered problems in a short story format. One of Gus’ customers did that.

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What if one car is positive ground and the other car is negative ground?
And your last connection shouldn’t be to a battery post.

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No, but you can boost a weak battery with a 12v source to get a car started. But you don’t want to charge it with a 12v source. Too much voltage drop, too much heat, battery can explode as others have posted.

No. As long as both are the same voltage. An alternator is just a more effective way of creating electrical power.

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When dealing with a neg ground car to positive ground car you must make sure cars are not touching. Hook up jumper cables to posts of the dead/low battery first. Then to the donor car, ground side last. Though jumper cable manufacturers usually instruct you to attach the ground cable to a ground point rather than the battery post, back on the rare occasion when I might jump a battery I preferred attaching directly To the terminals. Last hookup is to the donor car ground whether to the battery post or chassis.
But I do not jump start any vehicle scene the early 70s, too many systems that can be harmed.

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Negative to negative, positive to positive, regardless. I wouldn’t jump a 6v with a 12v.


Thank you all for the information. It’s not too likely that I’ll be in some parking lot when I run into someone needing a jump start for his bone stock 1950 Ford, but it’s nice to know I’ll be able to help in the off chance I do.

Thanks again.

Lol, other positive ground cars out there, but you probably have to go to a classic car show to see them. I think the Brits continued with positive ground into the 60s.