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Re: Jump starting a positive ground system

Subject: Re: Jump starting a positive ground system
From: "Roger Garnett" <>
Date: Fri, 13 Dec 1996 12:49:17 -0500
David Benner writes:

>  We want to try to turn over the engine but if it is stock and has a pos.(+)
> ground I am not positive(No pun intended) how to hook up cables. Any help
> will be appreciated. Dave 72 

>From this summers issue of British Car Magazine (I've still got to make a web 
page out of this)

Jump Starting Your Car- Are You Positive?

by Roger Garnett

Positive ground cars used to be the norm, but have now become somewhat rare,
lurking in the shadows, waiting to confuse the owner, or tow truck driver of
the "modern world". Most British cars produce d before 1968 were wired
"Positive Ground", meaning that positive side of the battery is connected to
the chassis, while the negative side is used as the "hot". By 1968, the
standard was reversed, an d negative became the ground side for most new cars.
This was mostly to make wiring new electronic components easier.

Many choose to convert their car to negative ground, to avoid problems
installing sterios, and other electronic equipment. On many older cars, with
mechanical tachometers, no radios, or other polarit y sensitive components, the
polarity can be reversed by simply swapping the  battery cables, and
re-polarizing the generator. It gets more complicated if you have a later car,
with electric tachomete r, polarized fuel pump, and any other polarity 
specific devices. 

For those who either prefer to remain original, or just haven't converted yet,
there is often confusion when it comes time to connect jumper cables between a
positive and a negative ground car. "Was that ground to positive, or negative
to the frame, or hot to?" A few simple guidelines may help:

-Positive and Negative refer to the terminals on the battery, regardless of 
which way the car is connected.

-"Hot" and "Ground" refer to the wiring system of the car. If the car is
Positive ground, then Hot=Negative; and if it's a Negative ground chassis,
then Hot=Positive.

-While the convention is to use a red wire or jumper clip for positive, and
black for negative, never trust the colour of the wires on your car. Always
check the battery markings directly.

-Always make sure the jumper cable clips can't touch each other, or the car
body and cause a short circuit. Also, don't let the cars touch each other, to
avoid an unwanted connection.

-The single most important point to remember is to always connect the positive
battery connection on one car to the positive on the other, and likewise,
negative to negative.

-It's advised to first connect both cables to the "source" car, next the hot
on the car being jumped, and finally connect the ground on the car being
jumped to a clean chassis or engine ground point. This is to avoid making any
sparks near the battery, as there can be highly combustable hydrogen gas
coming from the cells of the battery.

-Once connected, it's a good idea to let the source car run for a few minutes,
to charge the dead battery somewhat, rather than tying to draw all the
starting current over the jumper cables. (Always use the heavist cables you
can get- anything less than 6 or 8 guage wire is good for charging, but not
stout enough to run a starter directly.)

-On many newer cars, it is advised not to run the engine while using them to
jump another car, so as to avoid voltage surges which might damage

-Removing the leads is the reverse of connection...

Thus, if you are trying to jump start your positive ground 1955 Austin from 
your 1995 Rover:
-connect one end of each jumper lead to the Rover's battery terminals.
-connect the other end of the negative lead to the negative battery terminal on 
the Austin.
-connect the other end of the positive lead to a clean chassis/engine ground 
point on the Austin.
-Run the Rover for a few minutes at about 2000-3000 RPM to charge the Austin.
-Shut down the Rover, and start the Austin. Remove the leads, and you're done.

Of course, you may still have to figure out why your battery went flat in the 
first place!

Copyright 1996 Roger Garnett

Don't forget to checkk out other tech articles on the British Cars Web:

 Roger Garnett  ( Webmaster

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