How ground is ground?

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

coughed up:
> 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.

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!"

coughed up:
> 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.

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!"

> 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

> 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

"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?

"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?

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/

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/

bank robberies.

Both charges were fabrications, even according to BATF Director John Magaw,
who admitted the accusations were "inexcusable" in testimony before Congress.

THREE HUNDRED armed federal agents conducted a siege of the Weavers' mountain
home, first killing Randy Weaver's dog, then his son, then his wife.

A law enforcement wilding.

* The CATO Institute, "Congressional Testimony", May 24, 1995
* http://www.cato.org
*
* The Marshals, wearing camouflage and carrying silenced machine guns, did
* not identify themselves or their purpose, but they did shoot one of the
* dogs. Sammy Weaver, fourteen-years-old, returned fire, and was promptly
* shot by a Marshal.
*
* Sammy turned and fled, with his nearly severed arm flopping as he ran.
*
* Sammy was promptly shot dead in the back.


An FBI sniper, Lon T. Horiuchi, testified he could hit a quarter at 200 yards.

* The CATO Institute, "Congressional Testimony", May 24, 1995
*
* An FBI psychological profile, prepared before the attack, called Vicki
* Weaver the "dominant member" of the family, thus implying that if she
* were "neutralized" everyone else might surrender.

Horiuchi shot Weaver's wife in the head while she held her b