remcow coughed up:
>> Is it possible that there is some signal ground that is different
>> that chassis ground that will hurt something else on its circuit
>> once the cig. lighter is used?
>
> Hey Tom
>
> I agree with Alan - don't see much reason for them to put ground in
> the fuse box. Unless you absolutely know that it is hard-tied to
> ground, I wouldn't use it.
>
> There may be a difference in where you tap your ground, depending on
> what type of equipment you want to install:
>
> For instance, if you need ground/power for a two way FM radio, the
> best spot is the ground/power lug of your battery. Tapping it
> anywhere else and you'll have currents with other devices in common.
> Quite often you'll hear the alternator's generated AC component
> superimposed on the transmitted signal. On the other hand, AM/SSB
> transmitters or audio components (Radios and amps) could also have
> similar artifacts in their audio, but may be less noticeable because
> of the basic technology used. I had a Saab once that had a slight
> alternator whine on its speakers, regardless of my volume control
> setting -- since it was a relatively low power device, a simple choke
> killed the noise.
>
> If you are running something like a GPS or PDA, grounds don't make
> much difference since devices like that usually run indirectly off
> the 12V power through a regulator or switching power supply -- these
> introduce typically a lot of isolation and so any noise picked up
> will not make much difference.
>
> What are you trying to hook up?
>
> Regards,
> Remco


I am turning my cig. lighter into an "always on" or "always hot" or "battery
direct connect", or what have you.

What I find confusing about these answers of your's and Clarence's is that
the options connectors are designed for additional equipment to be attached.
At the far left there is a 3 blade connector socket on the options connector
block, which seems to have the center be power and the other two are ground.
Presumably for something known device that needs both power and ground.
Perhaps one of the blades is ignition, to complete the triad: [always
on]power, ignition, ground.

The other problem I have is how can that ground connection actually be
something like the rear window defroster. Wouldn't I be measuring the ohms
as /resistance/ and isn't a heating coil like that designed around the heat
produced by resistance, as in a toaster? I guess I'm not sure I understand
how that would be 0.

But I trust you all----it's the point of me asking the question in the first
place. I'd like to know what that 3 blade connector thing is for if not to
supply a usage ground (with power) to something. It looks like a dedicated
thing.



--
"Gentlemen, you can't fight in here! This is the War Room!"