[mij_nagrom88]

Wanted to get peoples input on procure grounding to the front of the vehicle with a trunk located battery. What would be the pro pure place to get good grounds. I seem to get 11.45v at the fuse boxes in most cases. Seems if I had better grounds that I would get a better voltage reading. Correct me if I am wrong. I don’t see a lot of ground straps anywhere on the driver side.

 

[rkupon1]

Mine is grounded to frame rail under trunk pan

 

[Mike Goble]

The frame closest to your battery is the best place to ground. Make sure you have a good ground to the engine block from the frame as well. Once you start your car, the main ground is the case of your alternator, so if there is no problem starting the car your battery ground is sufficient.

 

[Custom Jim]

When you are getting 11.45V at the fuse block what are you getting across the battery ?.

What is your voltage at the back of the alternator ?.

When you are taking measurements, are you also moving the ground point for the meter ?.

You could have a power delivery issue and/or a ground issue.

Maybe do a check and see how much voltage you have between the battery negative post and to a ground spot up front.

Maybe too go through all of your connections and clean them and make sure they are all good and tight.

Some people run a ground from the trunk battery to something like a rear frame rail or somewhere else in the back, then run a ground from the firewall to the engine. Some will run a dedicated ground from the battery to the engine.

You will get some increased resistances when using the body of the car for a ground path from one end of the car to the other and this is due to all of the spot welded together metal panels as it is not just one piece of steel from the taillight panel to the firewall.

Jim

 

[Mike Goble]

"Steel has a conductivity much less than that of copper, with copper at 58.5 Siemens/m and carbon steel at 5.9 Siemens/m.
The other factor is the cross sectional area of the conductor, with larger CSA conductors being able to carry more current. The CSA of the copper wire you run from the battery to the block is well defined by its diameter. The CSA of the steel conductor basically involves every piece of conducting metal that interconnects to any other piece and runs from the battery connection in the rear to the block connection in the front. Frame rails, floor pan, body panels, roof, any metal to metal connection, which makes for a CSA many times larger than the copper cable.

As I have pointed out before, this ground path is most important when you are starting the car as the battery is the source of all the current. Once the alternator voltage exceeds the battery voltage the ground becomes much less crucial, carrying only the charging current of the battery. Bottom line is - if you turn the key and the car starts readily, the ground connection is sufficient.

Ground-Frame vs engine

Found this in an article with wiring expert Ron Francis. Copper Conductivity Directly related to the grounding issues are those induced by poor battery cable connections. Bowers tells us that many installers still ground the negative battery cable to the frame of a vehicle, but there’s one...

www.stevesnovasite.com

 

[mij_nagrom88]

"Steel has a conductivity much less than that of copper, with copper at 58.5 Siemens/m and carbon steel at 5.9 Siemens/m.
The other factor is the cross sectional area of the conductor, with larger CSA conductors being able to carry more current. The CSA of the copper wire you run from the battery to the block is well defined by its diameter. The CSA of the steel conductor basically involves every piece of conducting metal that interconnects to any other piece and runs from the battery connection in the rear to the block connection in the front. Frame rails, floor pan, body panels, roof, any metal to metal connection, which makes for a CSA many times larger than the copper cable.

As I have pointed out before, this ground path is most important when you are starting the car as the battery is the source of all the current. Once the alternator voltage exceeds the battery voltage the ground becomes much less crucial, carrying only the charging current of the battery. Bottom line is - if you turn the key and the car starts readily, the ground connection is sufficient.

Ground-Frame vs engine

Found this in an article with wiring expert Ron Francis. Copper Conductivity Directly related to the grounding issues are those induced by poor battery cable connections. Bowers tells us that many installers still ground the negative battery cable to the frame of a vehicle, but there’s one...

www.stevesnovasite.com

I guess what I am getting at is shouldn’t I have the same voltage at the fuse box as I would at the battery?

 

[Mike Goble]

Not if there's any current flowing. If you are measuring the voltage with the key off and the doors shut it should be pretty close.
When you do your voltage measurements, use the same ground point for all measurements, especially if you suspect a faulty ground. If you suspect that your ground from your trunk mounted battery is faulty, attach a long wire from the battery negative terminal to the negative lead on your meter, then turn on all electrical items that will run without the engine running. Using the long wire as your ground reference, measure the potential at the block and any chassis ground at the front of the car. Ideally it should be zero, but if it's less than 0.1v you should be good.
Once the engine is running, the battery ground only carries the charging current for the battery as the rest of the current returns to the case of the alternator. You want good grounds from your block to the frame and any sheet metal that has a ground attached to it.

 

[Bob's 65 Post]

In a perfect world you would get the same reading at the fuse box as you would at the battery, but the ground path is probably not zero resistance (ohms).
Try this simple experiment which is very simple and fast. Take a piece of #14 or #12 insulated wire and cut it about 20'. Now connect one end directly to your negative battery terminal, and use the other end as your ground to your test meter and check your voltage at the same locations you did before. You should get the same reading you do at your battery posts. If you do, you need to add more and/or better bonding straps and jumpers between body and frame parts to improve your ground path. Doing this will eliminate the resistance that is dropping your voltage.

If using the test jumper you still don't get the same voltage as your battery output, you have corroded terminations, fuse holders, splices, etc., related to the positive side of your circuits.

You can also do as Jim recommended above, and use this jumper from your battery ground and go to various locations on your car and take resistance (ohm) readings (not voltage) between your car body and frame and the jumper wire and see how the resistance varies at different points to get a better idea of where you need to add jumpers. The higher the ohm reading is where you need to improve grounds, add jumpers, etc.
My trunk mounted battery is grounded to the frame in the rear, then up front I have a heavy jumper from the frame to the block, frame to firewall, and frame to radiator support.

I hope this all makes sense. If not, let's hear your questions, and some of the test readings. Great looking 65 post! Let's see some more pictures?

 

[Bob's 65 Post]

I guess what I am getting at is shouldn’t I have the same voltage at the fuse box as I would at the battery?

So what did you find?

 

[bruinfan1966]

If you really want to do it right (if not you will always have issues) run a negative cable all the way to the engine block, it may be a pain but it will be far less of a pain then the electrical gremlins you will never get rid of. The full frame cars are a different story, on my 55 I ran the cable from the trunk mount battery to the frame in back then from the frame up front to the engine block and my voltage at the fuse block was exactly the same as the battery. When I built the Nova I knew better and ran both positive and negative 1/0 battery cable to the starter motor and engine block and my voltage is the same at my fuse block as at the battery, I also ran a ribbon ground from both the left and right sides of the engine block to my IFS then another from the block to the firewall. I also ran a battery cut switch on the negative cable close to the battery in the trunk, I do not go through the trouble of the tunk mount solenoid switch since running the negative cable to the block will eliminate the heat soak issues so many people run into.

 

[Mike Goble]

There is not a single OEM rear battery installation that doesn't use a grounding point on the frame close to the battery, including BMW, Mercedes, Volvo, Chrysler, Jaguar, Ford, Saturn, etc. None of these manufacturers run a separate ground cable because the steel of the car is a much better conductor. Most of the problems stem from poor connections at the cable/frame interface.

 

[Rusty63]

as shown in the photo below, my battery ground doesn't go to the frame, but the car starts with no issues.

based on my understanding of what Mr. Goble says, if the car starts, it is a decent enough ground. therefore, the wheelhouse is a viable location and no need to move it to the frame?

Sorry to jump in but it seemed related and may help others.

-Rusty

 

[Mike Goble]

No matter where you mount your ground cable the surface to surface contact area is the same. Once you get past the small area where the cable contacts the steel, the current disperses in all directions based on the conductivity of the path.

For simplicity's sake let's say that you attached your copper ground cable to your flat 1/16" steel trunk floor. The conductivity of the copper wire is 8 times the conductivity of the steel floor, so there is a point at which the cross-sectional area of the steel becomes >8 times the CSA of the cable.

Let's use a 1/0 cable as our battery cable - the CSA of 1/0 cable is 0.083 square inches. We need to calculate the radius of a 1/16" cylinder whose wall area is 8 times the 0.083 square inch CSA of our wire, or 0.664 sq. in.

The basic formula would be 3.14D/16 = 0.664.
Transposing the terms gives us D = (16 x 0.664)/3.14 or D = 3.38" and the radius of the circle would be 1.69".

This means that at a distance of about 1.7" from the connection point the resistance of the steel path of conductivity becomes less than the resistance of the 1/0 cable. It's easy to see how the steel path is orders of magnitude less resistance than the cable as the CSA of the steel becomes ever larger.

 

[bruinfan1966]

There is not a single OEM rear battery installation that doesn't use a grounding point on the frame close to the battery, including BMW, Mercedes, Volvo, Chrysler, Jaguar, Ford, Saturn, etc. None of these manufacturers run a separate ground cable because the steel of the car is a much better conductor. Most of the problems stem from poor connections at the cable/frame interface.

Actually you are incorrect, the oem's do it because its cheaper, the car's steel is not a better conductor and even more so when that steel is 50 plus years old. You are always better off running two separate cables to the point of termination, As a ASE Master Tech as well as master tech for both Honda and Lexus I can tell you that any important system will run both cables, I usually don't come on any forum and debate with anyone but 40 plus years in this trade every day of my life (plus being that go-between the factory and field techs) pretty much qualifies me as an expert.

 

[Mike Goble]

I confess that I am not a master mechanic with 40 years experience, instead I have to fall back on 55 yrs of electronics experience and a degree in Electrical Engineering.

Let's clear up a couple of points:

1. There is no expiration date on the conductivity of steel. 50 year old steel conducts at the same level as new steel.
2. The cross sectional area of a conductor defines the resistance per unit of length, commonly shown in wire tables.

3. One reason copper is used for wire is its high conductivity. A steel wire used to carry the same current would have to have 8-10 times the CSA to accomplish the same electrical end, i.e. voltage losses and heat generated. If I can use a steel conductor that is 20 times the CSA of a copper one, I will have superior electrical performance.

What is the average CSA of the sheet metal of a 1-2 gen Nova? This would include any and all electrically connected sheet metal from the front to the rear. I won't include any weld-in subframe connectors or roll bars. Rough measurements of my wagon indicate a floor width of about 5' and a roof about 4' wide.
The floor is 16 gauge, so a 5' wide section of it will have a CSA of about 3.75 sq. in. This is just the floor, not including the sills, subframe members and any other bracing.
A 48" wide 20 gauge steel roof has a CSA of 2.4"
Just the sheet metal of the floor and roof has a CSA of over 7 sq. in.
Compare that to the CSA of a 1/0 gauge wire - 0.083 sq. in.
Just the sheet metal has a CSA 74 times that of the wire. If you put a 1/0 copper wire in parallel with this, the copper would only carry 10% of the current because the steel presents the path of least resistance. Electricity doesn't care what the conductor is made of, it chooses the path of least resistance.

In order to create the situation where the steel is a worse path than the copper you would have to have lost well over 75% of the sheet metal. I've seen some rusty cars in my life, but that would be the worst.

I'll agree that using the frame as the return path is cheap, but it is also the most effective way. We're not discussing later cars where the body panels may be glued on or made of non-conductive materials, we're dealing with old cars with hundreds of spot welds holding a steel body together.

Actually, the worst path into the battery is the positive cable as it will carry much less current than the ground side for similar electrical losses.

 

[bruinfan1966]

I confess that I am not a master mechanic with 40 years experience, instead I have to fall back on 55 yrs of electronics experience and a degree in Electrical Engineering.

Let's clear up a couple of points:

1. There is no expiration date on the conductivity of steel. 50 year old steel conducts at the same level as new steel.
2. The cross sectional area of a conductor defines the resistance per unit of length, commonly shown in wire tables.

3. One reason copper is used for wire is its high conductivity. A steel wire used to carry the same current would have to have 8-10 times the CSA to accomplish the same electrical end, i.e. voltage losses and heat generated. If I can use a steel conductor that is 20 times the CSA of a copper one, I will have superior electrical performance.

What is the average CSA of the sheet metal of a 1-2 gen Nova? This would include any and all electrically connected sheet metal from the front to the rear. I won't include any weld-in subframe connectors or roll bars. Rough measurements of my wagon indicate a floor width of about 5' and a roof about 4' wide.
The floor is 16 gauge, so a 5' wide section of it will have a CSA of about 3.75 sq. in. This is just the floor, not including the sills, subframe members and any other bracing.
A 48" wide 20 gauge steel roof has a CSA of 2.4"
Just the sheet metal of the floor and roof has a CSA of over 7 sq. in.
Compare that to the CSA of a 1/0 gauge wire - 0.083 sq. in.
Just the sheet metal has a CSA 74 times that of the wire. If you put a 1/0 copper wire in parallel with this, the copper would only carry 10% of the current because the steel presents the path of least resistance. Electricity doesn't care what the conductor is made of, it chooses the path of least resistance.

In order to create the situation where the steel is a worse path than the copper you would have to have lost well over 75% of the sheet metal. I've seen some rusty cars in my life, but that would be the worst.

I'll agree that using the frame as the return path is cheap, but it is also the most effective way. We're not discussing later cars where the body panels may be glued on or made of non-conductive materials, we're dealing with old cars with hundreds of spot welds holding a steel body together.

Actually, the worst path into the battery is the positive cable as it will carry much less current than the ground side for similar electrical losses.
[/QU

I confess that I am not a master mechanic with 40 years experience, instead I have to fall back on 55 yrs of electronics experience and a degree in Electrical Engineering.

Let's clear up a couple of points:

1. There is no expiration date on the conductivity of steel. 50 year old steel conducts at the same level as new steel.
2. The cross sectional area of a conductor defines the resistance per unit of length, commonly shown in wire tables.

3. One reason copper is used for wire is its high conductivity. A steel wire used to carry the same current would have to have 8-10 times the CSA to accomplish the same electrical end, i.e. voltage losses and heat generated. If I can use a steel conductor that is 20 times the CSA of a copper one, I will have superior electrical performance.

What is the average CSA of the sheet metal of a 1-2 gen Nova? This would include any and all electrically connected sheet metal from the front to the rear. I won't include any weld-in subframe connectors or roll bars. Rough measurements of my wagon indicate a floor width of about 5' and a roof about 4' wide.
The floor is 16 gauge, so a 5' wide section of it will have a CSA of about 3.75 sq. in. This is just the floor, not including the sills, subframe members and any other bracing.
A 48" wide 20 gauge steel roof has a CSA of 2.4"
Just the sheet metal of the floor and roof has a CSA of over 7 sq. in.
Compare that to the CSA of a 1/0 gauge wire - 0.083 sq. in.
Just the sheet metal has a CSA 74 times that of the wire. If you put a 1/0 copper wire in parallel with this, the copper would only carry 10% of the current because the steel presents the path of least resistance. Electricity doesn't care what the conductor is made of, it chooses the path of least resistance.

In order to create the situation where the steel is a worse path than the copper you would have to have lost well over 75% of the sheet metal. I've seen some rusty cars in my life, but that would be the worst.

I'll agree that using the frame as the return path is cheap, but it is also the most effective way. We're not discussing later cars where the body panels may be glued on or made of non-conductive materials, we're dealing with old cars with hundreds of spot welds holding a steel body together.

Actually, the worst path into the battery is the positive cable as it will carry much less current than the ground side for similar electrical losses.

I have a degree as well and while we could easily spend the day going back and forth with formulas ect. its really just all ego at that point as far as I'm concerned. From what I can see after reading posts and replies on this site for several years is that 90% of the members really just want to know what will help them get to the root of their issue. I'm sure they don't need me to give them a lesson on how to diagnose their problem with a picoscope which I do at a course I teach. What I have found is that if you tell a guy the best bet is to run a second wire to the front (he's already running 1) you are pretty much guaranteed to eliminate future issues. How do I know this? because I've built and/or repaired more street and race cars than most people ever will. I have found through experience that if you run a 1/0 negative cable from your trunk mounted battery right to the engine block and check you voltage at the battery, horn relay, junction block, and fuse box to ground you will have 12.6 volts with a fully charged healthy battery.

 

[Custom Jim]

I'll add something which I think a lot of us may not be realizing in that the steel we might be attaching to in the back of the car like the trunk floor is not one solid piece all the way to the front where another connection might be made in such a spot like the firewall. The body structure is made up of a BUNCH of stamped steel sections AND are not fully welded against each other but are SPOT welded together (and I have seen in spots on my 74 that some seams were brazed as well as being lead soldered).

I have to think when the car was originally put together the spot welds were as large as they could be as well as the metal also being as thick as it could be but sadly due to time, the size of the spot welds probably are getting smaller and the metal is getting thinner due to rust . Now I'll say right here, it may be of no concern but I have to wonder when issues arise, was the car metal in pretty decent condition or is it a rust bucket held together and things covered with undercoating ?.

Right here I will say I AM not doing the math with spot weld connection area's between two or more pieces of sheet metal.

I'll also add in that years ago when one replaced a quarter panel, a trunk floor, a main floor, a roof, or whatever it was spot welded or plug welded back in (and then even here, were there as many weld put back that were originally in an area ?).

Years ago too no one was glueing panels onto a car and I have to think that no power can flow through the glues that they are using today to repair vehicles. I could be wrong and maybe in the formulation there is a conductive material in it.

I think we are going to agree to disagree with no one right way of doing things.

I like to think that if I attach to a section of steel in the back of the car, it is then spot welded to another section of steel and then this piece is spot welded yet to another one and this is done many times over and over again and by the time one gets from the back of the car to the front and each of these connections will have some voltage drop across those connections. How much, who knows, and it could be a little and of no concern or could be at the point of concern.

Just like today working on a "Rat Rod" is that the headlights are in old Ford housings that are then attached to a bent steel tube and then bolted to a bracket welded to the frame. The headlights are bolted to a heavily primed and painted tube which is then bolted to a heavily primed and painted frame and I did not want to rely on using these connections for a ground path (the original owner had them grounded through a housing pivot bolt) so I then added to each headlight a dedicated ground which runs alongside the low and high beam wires and will end inside the car to a ground point. This was my call and think I went the right way while others may say just to let it ground how it would with things being bolted together and welded BUT I'm hoping not to have any issues doing what I did. Others might have gotten away with it that way but my luck is not that good.

Jim

 

[Chevy II Guy]

Take it from a guy that has learned this lesson the hard way. Run a heavy battery cable from the battery ground all the way up to your motor or transmission. The bell housing bolts are a good place. Then, install grounding straps from your motor to your frame and from the motor to the fire wall. If you do this, you won't have any problems. On the flip side, I have seen batteries grounded to the frame that worked fine. Some people get by with doing this for years... and then all of a sudden, they don't have a good enough ground to start their car. Notice on ANY vehicle where the factory grounds the battery. It is usually to the alternator bracket or to the engine block (and not the frame). They do this for a reason.

 

[Chevy II Guy]

One other thing, I originally had my battery (in the trunk) grounded to the rear subframe. I have welded in subframe connectors so I figured this was a good path. I could start my car with no problems. However, I was burning up alternators. Upon getting my 3rd alternator replacement under warranty, I went to a alternator/starter rebuild shop and asked a few questions. I described my problem to him and he immediately said, "this sounds like a ground problem." I then ran the ground battery cable to my transmission and have not had a problem since.

 

[swerv52]

I agree with the Chevy II car guy above. Just bite the bullet and run a ground strap up to the front of the car and be done with it. Detroit Speed sells a nice kit for relocating the battery.