How ground is ground?

1999 / Honda CR-V

At the top of the fuse block inside the car there are a bunch of options
connectors.

Some of you have seen my prior postings concerning turning the cig. lighter
to "always on".

The question is this:

I know which of these is powered by the battery, always on.

But for ground: If I discover one of these options connectors to be 0 Ohms
resistance (impedance?) from it to the chassis, can I assume that there is
nothing else "on it" and that it is OK to use as the ground for the cig.
lighter?

I want to avoid an ugly wire going to a chassis bolt.

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?

Thanks!





--
"It's easier to be terrified by an enemy you admire."
-Thufir Hawat, Mentat and Master of Assassins to House Atreides

In rec.autos.makers.honda Thomas G. Marshall . com> wrote:
> But for ground: If I discover one of these options connectors to be 0 Ohms
> resistance (impedance?) from it to the chassis, can I assume that there is
> nothing else "on it" and that it is OK to use as the ground for the cig.
> lighter?

What you measure as zero ohms might be the rear window defroster, window
motors, or any other low impedance load. I wouldn't expect to find any
ground pins on the fuse block. There aren't any in my 2003 Civic,
according to the shop manual.

> I want to avoid an ugly wire going to a chassis bolt.

There are many ground wires attached to bolts already. The existing 12v
accessory outlet goes to a ground right there behind the panel. Why are
you looking for a different ground?

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

In rec.autos.makers.honda Thomas G. Marshall . com> wrote:
> But for ground: If I discover one of these options connectors to be 0 Ohms
> resistance (impedance?) from it to the chassis, can I assume that there is
> nothing else "on it" and that it is OK to use as the ground for the cig.
> lighter?

What you measure as zero ohms might be the rear window defroster, window
motors, or any other low impedance load. I wouldn't expect to find any
ground pins on the fuse block. There aren't any in my 2003 Civic,
according to the shop manual.

> I want to avoid an ugly wire going to a chassis bolt.

There are many ground wires attached to bolts already. The existing 12v
accessory outlet goes to a ground right there behind the panel. Why are
you looking for a different ground?

--
---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5

> 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

> 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

Agree with Clarence, that is
Sorry, Clarence.

Agree with Clarence, that is
Sorry, Clarence.

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!"

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!"

In rec.autos.makers.honda remcow > wrote:
> 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

That reminds me of a point that I was going to make in response to the
subject line, but I got distracted by the content ;-)

How ground is ground? Not very.

In high powered radar systems, it was common to run a scope probe along the
edge of the chassis, on "ground", looking for signal. When you didn't see
any, you were at the failed stage of the amplifier.

Ground in automobiles is a nebulous thing. Watch the brake lights and
taillights that have strange interaction on almost any Volvo, and some
Cadillac Sevilles. As the driver steps on the brake, the taillight goes
out and the brake light comes on. "poor ground".

"The chassis" is probably a good ground, but that's sometimes hard to
locate. I can't recall which car I was trying to work on... Even the
metal parts of the dashboard weren't grounded well.

On the Honda Civic, there are huge reinforcing bars in the dash, that I
would assume were a good ground, and the return wire for the accessory
outlet bolts to that.

---
Clarence A Dold - Hidden Valley (Lake County) CA USA 38.8-122.5