It's not that it matters electrically, other than as a safety
precaution. If you put a wrench on the positive terminal first, you run
the risk of sparks flying if you allow that wrench to touch the chassis
while you are loosening the bolt. By undoing the ground terminal first,
you remove any danger of a short while working on the positive lead.

Likewise, attach the ground terminal last when connecting up a battery.
All this assumes a negative ground system, which all modern autos that I
know of use.

Mark

Jack wrote:

>Ok, I need help.
>
>In several manuals, including a Ford Owner's manual (forgive me) and a
>Haynes repair manual, I've noticed that they specify that the negative
>battery cable must be removed first when disconnecting the battery.  Why???
>
>What possible difference can it make which terminal is disconnected first???
> When I first ran across this, I ignored it as a harmless error by someone
>who didn't understand electrics, but now I find it in "professional"
>references.
>
>Help!  What am I missing?
>
>//Jack
>
>
>