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[Jimmy Jerms]

Does anyone know why the Haynes manual says that the Neg on the doner battery should be connected to the engine block on the vehicle to be started. I've always connected Pos to Pos - Neg to Neg and never had a problrm :-?

[ian6pot]

It will do the same thing but conecting to the block will eliminate any resistance in the neg batt cable

[Bandit127]

And possibly reduce the chance of cross connection at the battery.

[Malabo]

Not disputing the resistance possibility, being the last connection to make, any arcing/sparks are away from igniting any hydrogen around battery.

[rickyboy]

Not disputing the resistance possibility, being the last connection to make, any arcing/sparks are away from igniting any hydrogen around battery.

That's my guess as well, not that I've ever followed the Haynes method anyways.

[JasonH]

The reason for not connecting neg to neg and pos to pos at the battery is safety.

When jump starting you'll be stuffing current into the car battery and it will generate a lot of hydrogen.

When you disconnect the jumps lead there will be a spark, sometimes small sometimes large. If you ignite the hydrogen the battery will explode spreading suphuric acid everywhere.

If both jump leads are connected to the battery whichever one you disconnect first will spark - right in the area the hydrogen is being generated......

If you had connected the negative elsewhere in the engine bay it's safe to disconnect - but of course do it before the positive!!

[Phil B]

The reason for not connecting neg to neg and pos to pos at the battery is safety.

When jump starting you'll be stuffing current into the car battery and it will generate a lot of hydrogen.

When you disconnect the jumps lead there will be a spark, sometimes small sometimes large. If you ignite the hydrogen the battery will explode spreading suphuric acid everywhere.

If both jump leads are connected to the battery whichever one you disconnect first will spark - right in the area the hydrogen is being generated......

If you had connected the negative elsewhere in the engine bay it's safe to disconnect - but of course do it before the positive!!

You won't get a battery to explode that way, worst that will happen is any hydrogen that has escaped and therefore mixed with air could theoretically flash over, but in reality the amount released is so low you couldn't get a pop if you tried!