6volt 48 ford truck

Did you make a mistake, did you not mean a Positive (+) ground system?

All the cars I have worked on since the early '60s have been negative earth.......

I personally do not know anymore when the general change was made from positive earth to negative, 50's maybe? (One web site mentions 1950 and another 1960, to which I tend to agree!)

Here is a website that might help you in converting if there turns out to be a need (but not as you have written it).

The coil needs to be correct for the polarity, I never knew that, but it makes complete sense to me!! I wonder how many people with old positive earth cars have a (relatively) modern (negative earth) coils and get problems that they can never fix!!!!

Hello Andy G

Couldn't see website link - presumably it says the coil needs to be correct for the polarity. I didn't know that either and can't think of a good reason why it would matter, can you? But if system polarity is changed, to be on the safe side it would be easy enough to swap the coil LT connections so it sees unchanged polarity.

Re changeover, I had (in UK) a 1948 car that was +ve earth, also 1955 and 1956 ones, which I think were same, but I wouldn't swear to it.

Cheers........Codey

Many thanks, I completely forgot to include it it:-

Positive and Negative Earth Coils

Interesting, but I still don't get it!

It says "To identify the Coil - A Negative Earth car will have the Coil Secondary connected to the +ve Terminal of the Coil. A Positive Earth car will have the Coil Secondary connected to the -ve Terminal of the Coil" and this agrees with the circuit diagram. But it's no help in practice as the connection is inside the coil. You'd have to destroy the coil to find it. Coil terminals are marked +ve and -ve but that doesn't tell you where the connection is. I don't remember coils also being marked +ve or -ve earth, but then I haven't looked for a long time.

I didn't know it was important to get the polarity on the HT side right, and it's not at all clear to me why one polarity rather than the other should make the centre electrode run hot. But if we accept that, swapping the connections as my #4 ought to take care of it.

I suppose the bit about the burnt points problem could be right but I'm sceptical. With swapped leads the connection between primary and secondary is on the breaker side instead of the battery side but I wouldn't expect that to be a problem. There's only a few microamps in the secondary.

Cheers........Codey

I have found a common example that now sort of debunks the whole coil polarity issue all together.

Check out any newer vehicles with the coil pack ignition systems. Many of them have the secondary completely isolated from the primary and vehicle and fire two spark plugs together at the same time. If you disconcert one plug wire the other side wont fire either. This is also true on many smaller two cylinder lawn and garden, motorcycle, and utility vehicle engines as well. Many of them use one ignition coil to fire two cylinders.

As far as the points burning issues a lot of that comes down to mismatched coil and condenser sets. Or just cheap or wrong coils that have too low of primary resistance or are simply supposed to have an in line ballast resistor with them that was either never installed or more often was eliminated when it burned out.

Incomplete, incorrect, or just cheap parts causes all the points burning and weak spark issues I have ever dealt with.

You have added some modern, probably to my mind irrelevant data to the pot, but a "debunk" it was not. It had little or nothing to do with the problem to my mind at least....sorry to step on yout toes....

Concerning your last sentence alone, implies to me that you have had little or no experience of older vehicles with positive earth and or 6 volt systems, which precludes your seeing the possible problems we are discussing here.....not your fault in any way either.....

If you have worked ONLY on -ve earth, 12 volt systems, then your last sentence would be fully correct.....many REAL mechanics around today can only say exactly the same with total accuracy.....so don't be upset!!

6 volt systems (which is what we are talking about here!), as far as I am aware, whether positive or negative ground, never had coil ballast resistors. (Never is a word I seldom use as it can be wrong, but use of a ballast resistor on a 6 volt system would imply a 3 volt , or so coil, not very efficient I would guess.....but still possible!)

Ballast resistors allowed what is generally accepted as being able to use a 6 volt coil on 12 volt systems. Often the ballast resistor was shorted out when using the starter, so that the full available battery voltage, often only 7 or 8 volts whilst cranking in winter etc etc., could keep the spark at its normal good level, so that the motor had a better chance of starting.

Ford UK had a special name for it (they had massive starting problems in winter in the 60's and early 70's till they installed it!), but I have forgotten the name used....sorry.

Once the starting/cranking was stopped (usually because the motor was now running) the ballast resistor was placed back in circuit to stop the 6 volt coil overheating on 12 volts......

The explanation on this website about what happens when using an incorrectly polarized coil:-

Positive_and_Negative_Earth_coils

.....I personally find very easy to understand, though the idea of the pencil to determine the direction that the electrons are taking to be less well explained..... perhaps someone else could either improve on the explanation, or give another method of checking the direction of electron flow.....

Here is one from me, but assumes that a good low ohm ohmmeter is available for use....

To my mind, you only need to identify the point at which the secondary is attached to the primary, maybe using a micro ohm meter (I do not have a coil to hand to see if the difference is obvious enough when using a standard ohmmeter or not, sorry), the lower reading taken between the HV connector and the other two connections, being the end to connect to the power.

The other end then goes to the Breaker contacts......if its a coil for positive earth, this end (the end NOT connected to the secondary) will be marked +, and if its for a negative earth system, this point will be marked with a -....

Generally speaking, the resistance measured over a 12 volt coil's primary, including also 6 volt coils with a ballast resistor, will be around 3 - 3.5 Ohms, more or less will cause further problems.(Which also implies that a 6 volt coil with have around 1.5 to maybe 1.75 ohms primary resistance.....!)

I got this tip from a .pdf file at:-

http://www.newtronic.co.uk/new/support/lumign/optron/TB6.pdf

Some coils are clearly marked SW and CB, being the SWitched voltage for the ignition and the Contact Breakers, so you should have no problems in identifying the two connectors on such a coil...provided you know as to whether it was made for + or - earth as well.....! Using a good ohmmeter as I mentioned earlier....

I feel that using the info now contained in this post and having a suitable ohmmeter available (and knowing exactly how to use it!), anyone should be able to identify a coil as being for either 6 or 12 volt systems and also to identify it as being built for positive or negative earth systems.

Older VW Beatles were also 6 volt, so coils built for them might be suitable for other 6 volt (or 12 volt with a ballast resistor) vehicles, but I do not know off hand if they were positive or negative earth anymore, sorry.....

Up till now I have not seen or read a better more exact explanation than the one in the first link I posted above, but I am ready to learn IF someone comes up with one......

Quoting here from the easy to understand relevant passage from that website:-

Coil Misuse:

Using a +ve Earth Coil in a -ve Earth Car will seriously burn the points and cause the Capacitor to fail.

This is caused by the excessive Voltage that appears on the Coil -ve terminal by the Secondary winding.

Using a -ve Earth Coil in a +ve Earth Car will seriously burn the points and cause the Capacitor to fail.

This is caused by the excessive Voltage that appears on the Coil +ve terminal by the Secondary winding.

If the Coil's Secondary winding is connected to the Breaker Point side of the Coil, the Voltage swing will be larger than the points and Capacitor can handle and they will soon fail. This is the usual outcome for interchanging the coils.

I've worked on too many positive ground 6 volt systems to count actually and countless magneto systems as well. My experience is more from farm machinery but still with enough old cars and farm trucks systems tossed in to be able to feel quite comfortable with them also. Heres what I have learned over the years.

The condensers on many of the old style ignition systems are polarized and have a simple plus or minus sign stamped onto them if they are, however some are nonpolar also. Hooking up a positive ground condenser in a negative ground application is not any different than doing it with a an electrolytic capacitor in electronics. They fail fairly quickly afterwards. That tends to cause problems with points burnout and weak spark being the simple LC tank circuit that the coil and condenser make is not able to work or stay tuned properly. Without the condenser working properly the inductive kickback of the coil shoots across the points instead of being directed into the condenser or being passed to the spark plugs creating oxidation and hot points that burn out rather fast.

Maybe what you have worked on did not have inline ballast resistors but I have found diverse enough range of old 6 volt systems that did have and need them to ever write them off as not being apart of a system. I have found that in a number of old vehicles and trucks and a few farm machines they where up under the dash and very few people ever knew about them. A few where attached to or beside the coil them self. But still they are not an uncommon thing to find.

For basic examples some of the International machinery and trucks, some of the old Ford 2N, 8N, and 9N tractors have ballast resistors on the 6 volt positive ground systems as do many of the other brands of tractors and farm machines have them as well. In some old cars and pickups they used resistor wire instead of a ballast also. You very well could have been working on a ballasted 6 volt system and not even knew it!

Even today if you talk to the right parts guy and ask for a 6 volt coil they will ask if its a ballasted or un ballasted system. Back in the day many people had the ballast resistor simply burn out and they removed it and never figured out why they needed to change points and condensers every year after that.

I know positive and negative ground electrical and ignition systems far better than most. And I have much experience with things that very few people do today thanks to two grandpas and a good number of older friends who worked around this stuff for most of their lives when it was still common. I learned much of it from them working by their side as a kid and expanded on that knowledge with more modern principals as I grew up.

Its not uncommon to find me at an antiques show fixing someones 80 year old magneto or ignition system either. (I collect them by the way) I am happy to do it and thrilled to solve some experts problem with common sense and reasoning plus the occasional odd scrounged part that couldn't possibly work since they knew everything anyway except for that part about how to fix it of course!

When I do system change overs to 12 volt negative ground systems with alternators I always put in 12 new volt internally ballasted coils with the correct matching condenser if they need one and typically all new wiring for the ignition and charging systems at minimum. I never try and reuse that old stuff. For a few dollars more its just cheap insurance.

Don't worry no toes where hurt here. I have steel toe shoes on just for when the self proclaimed experts come a stomping! I have had enough hands on and learned education on this sort of stuff to know that when the experts cant figure something out they can come to me!

I figured what I had posted earlier was enough and just didn't think that I needed to do a class on the how and why details though.

What you have written here is "How much I know and how good my experience is", all well and good and quite interesting, but none of it (except maybe the point that some caps are marked + & -, though I have never actually seen one so marked myself) actually helps the OP in the slightest.....

I think that I at least managed to give the OP some methods whereby he can help himself a little bit further, which was my intention.

How about you giving him (the OP) some benefit of your vast knowledge in such a way that he can actually use it to help himself right now......and maybe I and a few others can also learn something useful too from you.

What you originally posted was simply not enough to be useful (nor here either really!), except maybe for an expert, and he would not need any help!

Simple it down by a large amount - K.I.S.S.

Remeber, a personal history helps no one to fix anything.....not even you! Thats just establishing credentials.....no more, no less....

Thanks in advance.

Sure.

If its a 6 volt system that was positive ground and that was changed to negative ground it would be wise to check the condenser to make sure its a modern one. The old ones where in some applications polarity sensitive however all the modern ones I have came across now are non polar poly or mylar film type condensers. That also makes them smaller physically and gives them greater voltage tolerances as well. Most of them now are not all that picky about what voltage they work on either. Having the correct coil and ballast resistor if needed will make more difference in the points life and spark strength.

The old condensers had the polarity and voltage issues. However being that very few old engines are still running their original points and condensers its rare to find an original set now unless its a truck that has sat unused or minimally used for the last 30+ years.

Old farm machinery is typically where the occasional original parts are found even then they have been changed out a few times but with what where likely original factory replacement parts which may have still had the polarity markings. Unfortunately thats also where your most likely to find the miss matched parts and missing parts issues as well. You never know who may have done what to make it run well enough to sort of keep working over the years. Thats where I end up doing most of the difficult trouble shooting. Expecialy in hacked over magneto systems!

When doing a system voltage change its just simplest and easiest to get a new coil and points/condenser kit at the same time. A good parts place will be able to tell you if anything needs to be specifically matched up for your new voltage and polarity.

I hope this helps more.

Perfect!!!

Thanks.

I am the person with the 48 ford f1 truck, the negative ground system was done some 15 years ago, this is based on my inspection of the plugs, wires and dist. cap.

The truck starts and runs fine, therefore my major tune-up will use standard components listed for the truck, my parts man said to bring in the old coil, points, condenser and they will match it up, by the way it is mounted or should I say bolted to the block,

Finally I will take the number off the distributor and this will also confirm the selection of the internals such as points etc.

I agree, KISS is always good, we engineers and designers tend to over complicate the explanations we offer, but that being said its good to have opinions.

Flaresideone

all comments are appreciated. thanks much

Flaresideone

Replying :

I didn't know it was important to get the polarity on the HT side right, and it's not at all clear to me why one polarity rather than the other should make the centre electrode run hot. But if we accept that, swapping the connections as my #4 ought to take care of it.

I have experimented this by mistake during 1970's.

I had a (+) ground English car. Needed to replace the HT iginition coil, with a new one. Found a German made new ignition coil in a near auto parts seller and fitted it on the car. However I did not care abt. the polarity marked on the casing of the coil.

At first 5 minutes the motor started and worked good as usual.

When I switch off the engine after five minutes, I remarked a powerful "hhsssss" sound. I checked what is happening. Found the HT Coil got warmed, the insulating oil inside was started boiling. It was nearly to explode due the internal pressure of gas formation. It was almost a bomb, ready to explode with hot boiling oil inside.

By this way I have learned about the importance of the polarity at the 12 V terminals of HT coil.

Regards

Hello Nezihozfirat

Can't argue with facts, there was clearly a problem, but it wasn't necessarily a case of wrong polarity.

Was the replacement coil 12 volt or 6 volt ?

Was it a coil for a nominal 12 volt car, but to be used with a resistor? (as described in posts by tcmtech and Andy Germany) I'm not sure what voltage, if any, is written on the coil with this system.

Was the coil designed for +ve or -ve earth? (assuming there is a difference, which I'm not convinced about)

Apart from the above, it's possible it was just a faulty coil.

Presumably you cured the problem - what did you do?

Cheers...........Codey

Hello Codemaster.

Herebelow are the replies for your questions . I remember all the facts even the passed long years

1. There is no doubt the new coil was for 12 Volt. It was hard to find a 6V coil at that time, because all the cars have turned to 12V years ago.

2. Thanks for your reminder for the series resistor. The original coil, I have removed had a resistor. It was an English Mallory (If I am not wrong) and had a series resistor. The one I found and replaced was a German Bosch. I have been told that no series resistor is needed for this coil. Therefore I did not connect a series resistor.

3. The first English coil was (+)ve. However the new German coil was (-) ve. I believe this is the startpoint of the problem.

4. The coil I replaced was brand new. I removed it from it's package.

How I have cured the problem was by reversing the 12 V terminals. ( + terminal to the ignition, and (ign) terminal to +. )

However the metal casing of the coil was compulsory connected to the metal body of the motor compartment, of which is connected to the + side of the battery.

It worked almost four years after I cured the problem as mentioned above. It was easier to start the motor, without using a series resistor.

Thanks for your interest on this problem

Kindest Regards

Farmall tractors used 6 volt positive (+) ground systems.

The first and most important reason for NOT doing a positive + ground is that your tractor will simply rust to brown dust if you do so. The -ve earth is a way to slow corrosion using the battery potential to avoid production od M+ ions.

So while electrical compatibility may be a diff issue. DO NOT change the -ve earth system.

If you want some entertainment go over to www.electro-tech-online.com. There is a guy with a positive ground land rover thats having rusting problems, being he converted it to a negative ground system a number of years ago, that will argue just the opposite!