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Old 28 Nov 2004, 03:45 pm
Thomas G. Marshall
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Default 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


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Old 28 Nov 2004, 05:07 pm
dold@XReXXHowXg.usenet.us.com
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Default Re: How ground is ground?

In rec.autos.makers.honda Thomas G. Marshall <tgm2tothe10thpower@replacetextwithnumber.hotmail. 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

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Old 28 Nov 2004, 06:57 pm
remcow
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Default Re: How ground is ground?


> 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




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Old 28 Nov 2004, 07:19 pm
remcow
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Default Re: How ground is ground?

Agree with Clarence, that is
Sorry, Clarence.



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Old 28 Nov 2004, 08:35 pm
Thomas G. Marshall
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Default Re: How ground is ground?

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!"


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Old 28 Nov 2004, 08:39 pm
dold@XReXXHowXg.usenet.us.com
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Default Re: How ground is ground?

In rec.autos.makers.honda remcow <whybcuz@yahoo.com> 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

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Old 28 Nov 2004, 08:47 pm
Thomas G. Marshall
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Default Re: How ground is ground?

dold@XReXXHowXg.usenet.us.com coughed up:
> In rec.autos.makers.honda remcow <whybcuz@yahoo.com> 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.


Interesting.

I think part of my problem here is that I don't have a solid understanding
of what the difference is between impedance and resistance. I'll have to
study this up more. 20+ years ago in college, the extent of my electrical
experience was EE. TTL circuitry and the like----wiring up flip flops and
all that. The analog universe I've learned on my own, which leaves
significant holes in my understanding.


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


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Old 28 Nov 2004, 09:21 pm
remcow
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Default Re: How ground is ground?

> I think part of my problem here is that I don't have a solid understanding
> of what the difference is between impedance and resistance. I'll have to
> study this up more. 20+ years ago in college, the extent of my electrical
> experience was EE. TTL circuitry and the like----wiring up flip flops and
> all that. The analog universe I've learned on my own, which leaves
> significant holes in my understanding.


Well, your background is better than most -- looking at both your and
Clarence post, I am assuming we all have an EE background?

Remember that the voltage drop across a wire (or chassis) is in direct
proportion to the current being drawn. So if you are grounding something in
common with a turn light, the drop you see across that path will be seen by
whatever is on that line. So, the supply voltage to your newly installed
device will modulate slightly and that could cause problems, depending on
what the type of device is. That's why it is good engineering practice to
bring your ground together at one point, close to the supply in most cases.
The signals are not electrically isolated but the current flows are kept
separate.

For your purposes, Clarence suggestion of using that huge bar is very
legitimate.

Regards,
Remco







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Old 28 Nov 2004, 09:27 pm
Randolph
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Default Re: How ground is ground?


"Thomas G. Marshall" wrote:
>
> 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 certainly *could* be a grounded options connector in the fuse box,
the fuse box already has ground for relays etc. It there *is* a grounded
options connector, it certainly would be a welcome change, But in three
different Honda's I have worked on there has not been a grounded options
connector.

> 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.


What Clarence and Remco are hinting at is that measuring small
resistances is difficult. A real ground connector will show a resistance
of more than 0 ohms to ground. You have resistance in the wiring and
connectors and resistance between your probes and what you are touching
the probes to etc.

With power turned off, many of the circuits in your car has very low
resistance. If you measure the resistance between the hot side of your
parking lights and ground with lights off, you are going to see low, sub
1-ohms resistances. A lot of places you measure will be
indistinguishable from ground with a simple ohm-meter measurement.

If you turn ignition to "on" and turn your parking lights on and then
measure the voltage between ground and those suspected ground
connectors, what voltage do you read? About 0 V or battery voltage?

The circuit diagram for the '97 CR-V shows one options connector that is
always on (C325), one that is on when the parking lights or head lights
are on (C326), one that is on with the key in Acc or Run (but not in
Start) (C327) and one that is on with the key in Run (but not in Start)
(C328). There could be more, the wiring diagrams
(http://www.hondahookup.com/manuals/CRV97wiring.zip) are tedious to
read. Your '99 may be different.

> 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.


Again, if Honda did include a ground it would be a very welcome change.
Also, I would like to see one that is on in both "RUN" and "START", not
only in "RUN", as this is needed by most after-market alarm system. In
my car I am fortunate enough to not have power windows, and the spot for
the power windows relay in my fuse box is a good place to get both
ground and "On-in-run-or-start"

Are you relocating the power outlet, and is that the reason you can't
use the existing ground for it?
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Old 28 Nov 2004, 10:43 pm
Thomas G. Marshall
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Default Re: How ground is ground?

Randolph coughed up:
> "Thomas G. Marshall" wrote:


....[rip]...

>> 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.

>
> What Clarence and Remco are hinting at is that measuring small
> resistances is difficult. A real ground connector will show a
> resistance of more than 0 ohms to ground. You have resistance in the
> wiring and connectors and resistance between your probes and what you
> are touching the probes to etc.


Ah, ok.

....[rip]...



> Are you relocating the power outlet, and is that the reason you can't
> use the existing ground for it?


Yes. I've had to give up on actually getting a hold of the existing in-dash
one for now until my service manual arrives. Here's my update post
explaining what I discovered. This CRV dash is much harder or at least much
"spookier" than the Buick Skylark, GMC truck, and Mitsubishi eclipse (which
is supposed to be a nightmare) that I've worked on ever were. That last one
is particularly surprising since all my "car" friends cringe at the mention
of the mitsu....there just isn't any room to do anything, on /either/ side
of the firewall.

http://groups.google.com/groups?dq=&....autos.honda.*

So now what I'm doing is simply attaching a new cig lighter socket (I have 3
cig. lighter plugs hanging around for various odd reasons) directly to the
always-on options connector. The new cig. lighter socket will hang out in
the drawer underneath the ash tray for now---my cell phone will be plugged
into that, and I'll shut the drawer, and have the wire for my cell phone
awkwardly hang out.

Gross, but it'll get me by.

I've been trying to get a read on what's safe and not safe to do, and it
really seems that using a bolt somewhere electrically connected to the
chassis is the best way to go. And probably the big arm thing that was
mentioned that holds the dash components in place.

I certainly *appreciate enormously* all the education you've given me in
this matter.

For the record, I'm not an EE guy, but as a software engineer, my CS major
required a moderate amount of EE, which is where my TTL and other digital
knowledge comes from.



--
Framsticks. 3D Artificial Life evolution. You can see the creatures
that evolve and how they interact, hunt, swim, etc. (Unaffiliated with
me). http://www.frams.alife.pl/


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