How to get a good ground in your Mopar

[Gryzynx]

I started to respond to this thread, http://www.forabodiesonly.com/mopar/showthread.php?t=141022
, and I realized it probably deserved a new topic.

There are a lot of electrical problems that trace back to poor grounds. Our 40+ year old unibody Mopars are particularly susceptible. I believe the problem starts with the factory layout for the negative side of the battery cable. The negative battery cable typically connects to the engine block at the front of the engine. A ground strap, (often discarded during engine swaps), connects the back of the engine block to the firewall. From there it is a series of welded and bolted connections to where ever the ground connection for any particular circuit may land. Corrosion and loose bolts ultimately lead to voltage drops causing dim headlights, noisy radios, etc.

Running a separate ground of appropriate gauge back to battery negative for all circuits would be the ideal fix, but this is not practical as it would result in doubling the volume of existing wiring in the car. My solution has been to bond certain areas like the rad cradle and the brake pedal/steering column bracket back to the negative battery terminal with 8 gauge wire. I use a long 1/4-20 bolt to provide a stud to which ground connections can be made in these areas. I will run a 10 gauge wire from the ground at the brake pedal back to the taillight area to ensure I have good grounds for my taillights. If I am running a battery in the trunk, I will use 00 cable, one run from battery + to the starter and one run from battery - to the engine block near the starter. + and - for the car then can be picked up off the engine block connections. No running the - connection thru the unibody structure for me! This, coupled with bypassing the firewall connector for the battery source/charging system will fix most electrical problems.

 

[slant6/4speed]

I try to run a single point ground system myself but that is due to the ham radio set-up more than anything. I run a ground from the block to the fire wall and from the alt. case to the fender. And one from the battery to the other fender/radiator support. And one from the hood to the fire wall (noise suppression) and I will run shielded ignition cables.

 

[67Dart273]

You said it, now you prove it:

How is having a completely separate ground system (these are not wood boats) better than using the WELDED unibody platform?

Can you prove this by means of accurate voltage drop testing? Can you prove it's more reliable?

I certainly can see your point about a separate, bolt on object such as the rad support, so DON'T use the rad support for a ground!! If you always use good connections to the WELDED central structure of the unibody, that is plenty good enough, and so far as RF noise, is probably better.

I would bet you money, that even CRANKING a big HP BB/RB, that you cannot measure the ground drop across the unibody proper AS COMPARED TO your advocated separate ground cable to the trunk.

 

[slant6/4speed]

From a RF point-if it is not grounded it does (or can) radiate noise-even the radiator support. Thats is why you ground all bolt on panels-fenders/hood/trunk lid. I do agree that to the unibody shell does not really need a ground run from the battery to the tail lights but there are reports of the tail light metal trim causing rf problems.

 

[Gryzynx]

You said it, now you prove it:

How is having a completely separate ground system (these are not wood boats) better than using the WELDED unibody platform?

Can you prove this by means of accurate voltage drop testing? Can you prove it's more reliable?

I certainly can see your point about a separate, bolt on object such as the rad support, so DON'T use the rad support for a ground!! If you always use good connections to the WELDED central structure of the unibody, that is plenty good enough, and so far as RF noise, is probably better.

I would bet you money, that even CRANKING a big HP BB/RB, that you cannot measure the ground drop across the unibody proper AS COMPARED TO your advocated separate ground cable to the trunk.

Should of seen that coming.

How is having a completely separate ground system (these are not wood boats) better than using the WELDED unibody platform?

It is not a completely separate ground system. What I advocate is bonding certain areas with adequate cable so you know you have a good ground.

Can you prove this by means of accurate voltage drop testing? Can you prove it's more reliable?

Yes and yes.

I certainly can see your point about a separate, bolt on object such as the rad support, so DON'T use the rad support for a ground!! If you always use good connections to the WELDED central structure of the unibody, that is plenty good enough, and so far as RF noise, is probably better.

Thank you, and I think we need to clarify that we are talking about typical Mopar unibody construction that has the rad support welded to the front frame rails and inner fenders. As an example, Mopar headlight wiring typically is grounded to the rad support, which was welded to the frame rails and inner fenders, which was welded to the firewall, which was bonded thru a strap to the back of the engine block, which was attached to battery - thru the battery cable. Add 40 years of rust and corrosion and any point of failure will affect headlight performance. Don't really care about RF noise at this point, but it is an added concern.

You place a lot of emphasis on welding. Welds can fail and in unibody structure, this can lead to poor electrical performance without detectable structural issues.

I would bet you money, that even CRANKING a big HP BB/RB, that you cannot measure the ground drop across the unibody proper AS COMPARED TO your advocated separate ground cable to the trunk.

Keep your money. I've made lots of it fixing this very problem for others. Actually, you are likely correct that you may have difficulty measuring a drop across the unibody proper, but the difficulty is in providing an adequate bond from the cables to the sheetmetal.

 

[skykeith]

Get one of these piloted brushes. They do an incredible job of removing all paint, corrosion, etc. and look much more professional than using a piece of sandpaper. Attach the terminal and cover the connection with something like LPS3. You won't have any problem with the connection.

 

[crackedback]

Put the battery in the trunk and run a single ground to the frame at rear and see how well the starter turns over. Then run a a direct ground wire from the battery to the block and see how that works. Even with the factory ground straps from engine to frame/body, they don't work as well as a dedicated ground. BTDT.

 

[67Dart273]

which was welded,............ which was welded ............40 years of rust and corrosion .................... Welds can fail and in unibody structure.

If all this welding, rust and corrosion is leaving parts of the unibody loose, then grounding is the last of your worries. The front end will evidently fall off the car.

you are likely correct that you may have difficulty measuring a drop across the unibody proper, but the difficulty is in providing an adequate bond from the cables to the sheetmetal.

The above I believe is the heart of the argument. 00 or larger copper is not cheap. Bonding the main battery ground to the trunk is just not that difficult. You can buy lugs with two bolt holes, or even weld/ silver braze a bolt/ ground plate to the trunk floor.

I don't have the money to go out and buy a whole bunch of cable and re-do testing that I did in 1972, but ohms law hasn't changed since then. Neither has the integrity of the unibody -- if it's still safe to drive.

The point is, just how far do you need to carry this? We are not talking about the space shuttle, here.

Tell ya what. In about a six months I'll probably be ready to trunk mount the battery in the 67. I still have a couple of great big carbon piles, and between the two of 'em I can put about 1000 amps of load on the system. Remind me along about September, and I'll do some serious testing.

 

[Gryzynx]

Get one of these piloted brushes. They do an incredible job of removing all paint, corrosion, etc. and look much more professional than using a piece of sandpaper. Attach the terminal and cover the connection with something like LPS3. You won't have any problem with the connection.

Very cool. Where do you get those?

Also don't forget the star washer between the terminal and the metal surface. The purpose of these is to bite into both surfaces to enhance the ground. They should not be installed with the intent of locking the screw head to the terminal.

Tell ya what. In about a six months I'll probably be ready to trunk mount the battery in the 67. I still have a couple of great big carbon piles, and between the two of 'em I can put about 1000 amps of load on the system. Remind me along about September, and I'll do some serious testing.

That ought to do it. With that kind of load, I'm pretty sure you'd be able to measure a voltage drop even across the cables. I'd guess you may likely see the most significant drop across the connections to the sheetmetal, but I'm sure if you must, and you are willing to maintain the connections, that such a setup will be servicable. My experience is that, much like Ohm's law, Murphy's law hasn't changed much over the years and the likelihood of a failure increases as your turn at the starting line comes up. Never say never.

.............. (.) (.)

I keep getting down to your signature line and I completely forget what was said!

Too much action going on for me to concentrate!

 

[green1]

Welds fail? Car fall apart?.
I hadn't worked on the Duster for 20 years, Installed a rear sub frame and trunk battery, grounded to new sub frame. Tried to fire it up; had forgot firewall to engine ground, smoked the ground at the heater. Installed a 10 from the firewall to engine. Went to the front of the engine, installed a battery cable to the k frame. Nice, now.

 

[fcm42000]

If all this welding, rust and corrosion is leaving parts of the unibody loose, then grounding is the last of your worries. The front end will evidently fall off the car..

whoa, wait a minute are you saying that the frame or connections (welds or otherwise) will be structurally weak if the resistance is high? Bologna

This isn't the first time you have had a response to a post that assumed a lot of variables, electrically speaking, and no we don't need your resume again, you worked on the first radars that ever existed, big deal.

I have first hand seen the benefits of bonding (by the way this is what the OP was talking about), so as far as proof goes, it is out there, you obviously have not done any work with it.

I like that you throw around terms like " ohms law" thats cute. Remember to use this elementary formula you need data, not guesses.


Gryzynx- I kind of have OCD with my machines and they may work ok as is but I progressively want them to be more efficient, so I like doing things like what you are talking about, it works.

 

[67Dart273]

whoa, wait a minute are you saying that the frame or connections (welds or otherwise) will be structurally weak if the resistance is high? Bologna.

That is EXACTLY what I'm saying, and since you didn't understand it the first time, I'll repeat. If the front section of the car ahead of the firewall has such rust problems THAT IT CANNOT CARRY BATTERY CURRENT enough to ground the block, and allow the starter to crank the engine, you'd better not drive it. Clear enough?

This isn't the first time you have had a response to a post that assumed a lot of variables, electrically speaking, and no we don't need your resume again, you worked on the first radars that ever existed, big deal..

It's called technical knowledge, and I don't appreciate your "summary." You weren't there, you have no freekin idea what I've worked on

so as far as proof goes, it is out there, you obviously have not done any work with it..

Once again, you weren't there. I HAVE checked this idea, the old 70 ran for over 4 years of constant driving with no attention other than possibly cleaning the battery, the posts, or replacing it. Back then, some of us rigged several cars with the same chuck of surplus mil spec wire--200 feet of it, all the same way. Care to guess what it weighed? My mind says 5 cars all grounded the same way, and all worked well.

I like that you throw around terms like " ohms law" thats cute. Remember to use this elementary formula you need data, not guesses..

In this discussion, Ohm's law is all we need. It's been around a very long time and it still works. No guesswork with it, either. The common term is "IR losses."

What we REALLY don't need here is your sarcasm. Nothing you offered in your post is factual. Nothing.

 

[fcm42000]

That is EXACTLY what I'm saying, and since you didn't understand it the first time, I'll repeat. If the front section of the car ahead of the firewall has such rust problems THAT IT CANNOT CARRY BATTERY CURRENT enough to ground the block, and allow the starter to crank the engine, you'd better not drive it. Clear enough?

The op mentioned nothing of a structure NOT carrying current, you assumed. If you have troubleshot electrical systems (not electronics on a bench) you would know that the most common faults are at connections. And in this case we don't know the true characteristics of the joints of the car, let me be clear, the car does not have to be falling a part to have bad grounding characteristics, we are not metallurgist who know the characteristics of the frame including the welds.

It's called technical knowledge, and I don't appreciate your "summary." You weren't there, you have no freekin idea what I've worked on

Well everytime something like this comes up you post pictures of an old radar building and say, look I know what I am talking about, sorry that just doesnt do it for me, posting a picture doesn't not justify an incoherent answer.


In this discussion, Ohm's law is all we need. It's been around a very long time and it still works. No guesswork with it, either. The common term is "IR losses."

What are you talking about? You don't have resistance values for his specific car for certain runs so you can't use the formula, period. hell you don't even know what voltage his system runs at, could be running high or low. So how do you impose you use this formula, not only that but why would you use it? are you going to go out to the car with a calculator and punch in numbers, sounds ridiculous. All you need is to check the resistance of bonded objects and personally deem what is ok and isn't, unless you have done a bonding check on his car with a proper meter you just can't assume

What we REALLY don't need here is your sarcasm. Nothing you offered in your post is factual. Nothing.

Not being sarcastic, just don't like seeing hipshot advice.

This is a unibody that acts as a common ground for the electrical system that is joined together with 40 year old welds with 40 year + old technology, by lazy factory workers, nuts and bolts that have been in place in some spots for decades and the current just happens to want to go through them with all there corrosion and muck, all these joints add up and slow things down.

I don't think the OP wasn't getting at this being necessary, just something to help people out who want to perfect something and you jump in and berate his claim, you don't always have to be so defensive, none of us know everything, maybe you could learn a thing or two.

 

[67Dart273]

Not being sarcastic, just don't like seeing hipshot advice.

This is a unibody that acts as a common ground for the electrical system that is joined together with 40 year old welds with 40 year + old technology, by lazy factory workers,.

Well, ya, you were. Go read what you posted. So once again I'll remind you. If a 40 year old weld is so rusty and weak that it cannot carry electrical current, it is not STRUCTURALLY sound, either. This is not hipshot advice. Back when I had access to stuff like milli-voltmeters I actually did some testing on this issue. You don't seem to want to believe this. So be it. This conversation is over.

 

[slantsixdan]

Evidence, folks. It's a wonderful thing. It has a nifty way of throwing dirt atop the coffin of dumb claims. What makes "body sheetmetal is a perfectly good ground". such a dumb claim is how easily it's disproven. You don't even need a meter! Put a brick on the brake pedal, get a long length of 14ga wire, put one end on the battery negative terminal and bring the other end to the taillight socket shell. See how the brake light gets brighter every time you touch the wire to the socket shell? Now why might that be? Is it:

A. Skyhooks
B. The taillight fairy
C. An optical illusion; it's not really happening because sheetmetal grounds are perfect
D. Increased voltage by dint of reduced voltage drop in the ground leg of the circuit

If you answered (A) or (B), quit bogarting. Puff-puff-pass. If you answered (C), you've made up your mind based on guesses, baseless opinions, and willful ignorance and you don't want to be confused with facts. If you answered (D), congratulations, you're using the brain god gave you for its intended purpose of thinking.

This reminds me of a particularly stubborn customer who wrote in complaining that ever since his '81 Thunderbird was new, the right headlamp was dimmer than the left and neither of them was very bright. He'd tried all the different sealed beams out there, he'd squawked to the dealer when the car was under warranty, he'd replaced the headlight switch and the high/low beam switch…no change. I sent him to this page and told him $49 worth of components and 90 minutes of his time would fix the problem. He didn't like that answer at all. Wrote back all insistent that Ford wouldn't put out a car with inadequate headlight wiring, and even if they wanted to, the DOT wouldn't let them, and that couldn't possibly be the problem, I was obviously just trying to con him out of fifty bucks, etc.

I told him he was wrong and I'd prove it by sending him the parts and only charging him if it fixed the problem. He agreed, with a few more smug comments about how I was wrong. I sent him the parts, and — big surprise, amigo! — two weeks later he's all up in my inbox amazed at how the problem was fully fixed, both headlights were now equally bright and much brighter than before.

(Evidence also does other nifty stuff, too. For example, this thread provides lots of evidence that putting 67Dart273 on my ignore list was a sound decision.

)

 

[67Dart273]

Evidence also does other nifty stuff, too. For example, this thread provides lots of evidence that putting 67Dart273 on my ignore list was a sound decision.

)

You also have provided no evidence. None. And just like the guy above, we don't need your sarcasm. If I'm on your ignore list how did you know what I said? So I'm only gonna say one thing. About your example on lighting, you are ......entirely.....incorrect...... Please go ignore.

 

[slantsixdan]

This message is hidden because 67Dart273 is on your ignore list.

 

[skykeith]

slantsixdan, since you have written the definitive lighting "Bible" we all must live by, you should know that all of your drawings show the headlights having a chassis ground. Your Japanese vehicle ground switched systems section is totally wrong. It says "now that you've used up your one and only ground wire on the 85 terminal of the low beam relay". Japanese cars have a low beam grounding wire and a high beam grounding wire. I wire all of my projects the "Japanese" way with the headlights hot all the time and the relays switching the ground side. It works great and pisses off all the Alpha Dogs who can't accept something different.

 

[fcm42000]

Thats why all electrical wiring is made of the same metal (steel) that your car is made of, it is such a great conductor, I can't figure out why they use that expensive copper stuff.

there is your sarcasm.

I work with electrical bonding at least once a week, mainly for rfi, but the lower voltage drops are a secondary benefit (for what I am doing). Maybe I should tell the engineers I work with what your thought process is so I don't need to listen to them. We use the most current milli ohm meters, measure down to the 10 thousandth of a milli ohm, micro ohms i think, and the tolerances are down to a hair.

Try dans idea with the long ground wire to the tail light shell, if that doesn't make a light bulb go off in your head (pun intended) don't know what will.

 

[slantsixdan]

slantsixdan, since you have written the definitive lighting "Bible" we all must live by

? Not really. Nobody's forced to take my advice.

you should know that all of your drawings show the headlights having a chassis ground

They're schematics. The text accompanying them talks about ground quality.

Your Japanese vehicle ground switched systems section is totally wrong.

That'll be interesting news to the many, many folks who've successfully used that "totally wrong" information to upgrade their Japanese vehicles.

I wire all of my projects the "Japanese" way with the headlights hot all the time and the relays switching the ground side.

OK. And…?

 

[67Dart273]

Thats why all electrical wiring is made of the same metal (steel) that your car is made of, it is such a great conductor, I can't figure out why they use that expensive copper stuff. .

I never said steel was equal to copper ON A SIZE BY SIZE BASIS. What I was getting at--and you know this full well--is that the huge surface area of the considerable bulk of the welded body is "plenty good enough."

there is your sarcasm..

and we don't need yours

I work with electrical bonding at least once a week, mainly for rfi, but the lower voltage drops are a secondary benefit (for what I am doing). Maybe I should tell the engineers I work with what your thought process is so I don't need to listen to them. We use the most current milli ohm meters, measure down to the 10 thousandth of a milli ohm, micro ohms i think, and the tolerances are down to a hair..

If you think that a what is essentially a once piece car body is NOT a good ground plane, you need your thought process changed. You don't need to explain to me about precision metering. Been there. As I said earlier, this is NOT the space shuttle, so just how PERFECT do you need to make it?

long ground wire to the tail light shell, if that doesn't make a light bulb go off in your head (pun intended) don't know what will.

I never once said NOT to ground the lamp shells, did I? I just don't agree you must run them clear back up front This is ESPECIALLY true if you are trunk mounting the battery


JUST HOW LOW does the resistance of a #14 lighting circuit have to be? I don't need a milli-ohmeter to determine that Let's say you have a 4-lamp stop/ tail group, with the legacy 1157 bulbs, and that you have the tail lamps on, and your foot on the brake.

Let's say, according to the lamp chart, that the bulb draws 2.10A .59A. With all 8 filaments lit, that's all of 5.38A

DO YOU REALLY BELIEVE that a unibody with properly made ground ties (I never mandated using factory sheet metal screws) is a better ground than 20 feet of what, no10?


So you can save me a hell of a lot of money buying milliohm meters, because YOU said you HAVE them. So here's what you do. Strap one of your nice expensive "most current" meters to a Mopar unibody, say, the right rear trunk floor, with a proper connection, then the other end at a convienient point up near the firewall, again with a proper connection, and you tell me what the resistance through the body is. I'll bet you money it's no more than 20 ft of no10 wire

 

[shadango]

GIRLS! GIRLS!!

You are both pretty, ok!?!?

Sheesh. LOL

Get one of these piloted brushes. They do an incredible job of removing all paint, corrosion, etc. and look much more professional than using a piece of sandpaper. Attach the terminal and cover the connection with something like LPS3. You won't have any problem with the connection.

Where did you find that? I likee!

 

[pauly v.100]

heres some...

http://www.aaabrasives.com/products/weiler/weiler_pilot_bonding_brushes_ep_series_-_stainless

http://www.westcoastbrush.com/powerbrushes.html

http://www.aircraft-tool.com/shop/search_result.aspx?CATEGORY=SHEET+METAL+TOOLS

http://cgi.ebay.com/Wire-Bonding-Br...raft-Tool-/350359270506?pt=LH_DefaultDomain_0

....now, back to my popcorn!!

 

[skykeith]

Yard store.com usually has the best price on wire bonding brushes.