Rick -
If you have a wire inside the wiring harness, it's safer to run a
power-switch circuit just in case it shorts with another wire in the
harness.
If you are running new wires outside the harness, it's safer to run a
ground-switch circuit because if it shorts out, it will likely short out
against the chassis, not another wire. If that happens, all that will
happen is the auxiliary item will switch on.
If you run a hot wire throughout the car and it shorts against the chassis,
you'll get a nice fire/smoke to cook your trout on.
Alan
On Sun, Oct 31, 2010 at 12:32 PM, Richard Ewald <richard.ewald@gmail.com>wrote:
> OK, I will bite, why is only a ground switched circuit "safe"?
> On production cars most non-computer controlled circuits are power
> switched. Computer controlled circuits such as injectors, idle motors, etc,
> may be either ground switched (pull down circuit) or power switched (pull up
> circuit)
> Ford uses (or at least used to) use pull up circuits on their fuel
> injection systems
> Bosch uses pull down circuits on theirs.
> Why is ground switched better?
>
> Inquiring minds want to know.
> Rick
>
> On Sat, Oct 30, 2010 at 9:23 PM, Alan Seigrist <healey.nut@gmail.com>wrote:
>
>> All -
>>
>> I have always wanted to use illuminated switches for my various auxiliary
>> items (the ones that light up when something is on), but they are all
>> wired
>> to only work with a power-switched circuit rather than a ground-switched
>> circuit.
>>
>> This is a major pain in the a** because if you want to do safe switching
>> in
>> a car, you should use ground-switch circuits.
>>
>> Do any of you know of illuminated switches around that will work with a
>> grounding switch? I can run a separate power wire from somewhere behind
>> the
>> dash if necessary.
>>
>> Ideas?
>>
>> Alan
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