There are basically two ways of installing a battery cut-off switch. One is
on the postitive battery line, and the other is on the negative. Assuming
you have a negative ground car, the preference is to put the cut-off switch
in the negative battery line as close to the battery as possible.
The reasoning here is several-fold. And most of this has to do with what
occurs if you've had a serious accident. First, if you disconnect only the
positive and do work on the car around the battery, if you accidently get a
wrench across the positive post and the body, you create a short with battery
explosion potential, and/or arcing that can ignite fumes or fuel. If you
disconnect the ground (negative side), then the battery is isolated from the
body and no short will occur if you accidentally touch it (or if the battery
is loose and hanging by its cables, for example).
ALso, if you run other accessories that remain powered with the ignition off,
you also positively kill power to them as well with the negative
disconnected, where you might have a low amp circuit that goes around the
kill switch for some items. This can cause potential back-feeding around the
kill switch, trying to send high current through the low current wires. If
they're not fuse or circuit breaker protected, then they could heat up and
start a fire. With a negative kill switch, is can be switched off (assuming
you don't run any secondary ground wires back to the battery...only the main
kill switch wire).
Regards,
Myles H. Kitchen
It is usually recommended that you also tape or otherwise insulate the
terminals of the cut-off switch if it is remotely mounted, so bent bodywork
or other metal can't short it out in a shunt.
Finally, also insulate or tape your battery terminals to minimize arcing in
such circumstances. An enclosed battery box is preferred.
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