The Stovebolt Site Forums The Shop Area The Electrical Bay Question(s) on my 55 12V converted ignition

Hi All
I have a 55 first series 1/2 ton C3100, 235 inline that is basically stock. I have had a few people suggest I consider changing my ignition coil as I have symptom of a bad coil ( stalls after prolonged idle, cools, then starts again- not fuel related) - I bought this truck early this year and have only taken it out a few times as the spring is unusually chilly here in Michigan. When I have started it it starts fine and has run well (except for the starter grinding a bit) The truck has been converted to 12V and I was thinking of replacing not only the coil, but the plugs, wires, coil, points, condenser, ballast resistor and possibly even the distributor cap. I am wondering though that since my truck was originally 6V, and now converted, is it safe to assume that the coil and ign is probably 12V? - if not, how would I test the ign components for 12V compatibility? and where in general is the ballast resistor on this vehicle? - I have barley had it out enough in the daylight to study the ign system and would like to verify a few things before I swap everything out so I know I have a system with parts in the condition I set, rather than guessing how old the plugs, wires, etc. are (although they look fairly new)

Thanks to all who respond

Joe

"Starts fine and runs well" = no modification required. You say it may stall after a prolonged idle; does it also stall out after a long drive?

The ballast resistor is on the firewall in the engine compartment (driver's side) on a 55.2, but I am not sure if this is also true on a 55.1. It's usually a whitish/ cream color.

Brad

When you hear your starter grind, it is taking metal off the ring gear on the flywheel. I would not ignore that. Mine did that because of a worn starter drive.

"The ballast resistor is on the firewall in the engine compartment (driver's side) on a 55.2, but I am not sure if this is also true on a 55.1. It's usually a whitish/ cream color."

1955.1 would have been 6v, originally.

Nonetheless, I have always seen/put a 12v-system ballast resistor on the upper firewall of an A-D truck that has been converted to 12v (as Brad posted was done on Task Force trucks). Is there an additional insulator/standoff for the attachment bolt?

But, here is a ballast resistor mounted on the coil-bracket .

https://www.chevsofthe40s.com/detail/19577/Coil_Chrome_Bracket_Only.html

Thanks- I was definitely unsure if 6V would have even had (to have) the resistor (originally).

1954 Shop manual ignition diagram (and 1955.1)
1955 2nd Series 6 cyl shop manual ignition diagram

Brad

Hi All
Thanks for the replies so far. As far as the grinding, I am well aware that my ring gear is bad. I took a look with the starter pulled and I have many rounded teeth - I am hoping to get by this driving season and then the winter project will be to replace the flywheel and maybe the clutch, since tranny has to be pulled to get to everything.

When it starts it does run fine and idles at a stop light OK - the single time it died it was idling over 7-10 minutes waiting for my daughter to come out for the ride she asked for - Has not repeated yet, but I have only driven her twice since the stall

As far as ballast resistor, I will take a look and replace if I find it. I am assuming at this point coil is 12V as well when I buy a replacement

thanks to all who have (and might still) respond

You want to make sure the starter and the ring gear are compatible. Very important so it doesn't keep happening.
http://www.devestechnet.com/Home/Flywheel

Brad,

Just to be clear: a 6v electrical system does not need a ballast resistor - it would used a 6v coil.

To be truthful, the 12v system uses a 6v coil too, but to avoid confusion, I like to go to rockauto.com and order the points, condenser, coil, cap, etc, etc for a 1956 Chevy Truck. That way there is no doubt about you getting the right thing. This is true for any auto parts store you go to. Ask for the ignition parts for a 1956 through 1962 and you will not be disappointed.

How does a 12v system use a 6v coil?

Do you mean a 12v system will usually/sometimes work OK with a 6v coil?

There are no 12v ignition systems prior to 1975. The ballast resistor steps down the ignition voltage to 6 volts and current to approx 4.2 amps. The math all works out perfect using Ohms Law. Since the 6 volt system doesn't require a ballast resistor, the ONLY thing that changed in 1955 was the ballast resistor. Adding it, meant being able to keep the 6 volt ignition system production line working clear into the 70's. Just replace your 12v system's coil with one of your 6 volt systems coil and there will be no difference in performance. Of course I have already done this and it all works out.

It also has to do with the time allowed for a single charge from the coil. Each time the ignition fires, there is only a short amount of time for it to recharge and fire again. Both the 6 volt and "12 volt" coils require the same amount of time and even the same high voltage result. You can take a 1950 6 volt coil and replace it with one that is stamped 12V and it will run exactly the same. Best I can tell, the resulting confusion was why the manufacturers stamped 12v on the coils in the first place. Of course this will be controversial, but once you do the math, it's over. Not that there may have been technology improvements to enhance firing in the 40 years or more, but check it out.. they work exactly the same.

This is why HEI is so popular. It reduces the amount of time it takes for the coil to reach its max firing potential an order of magnitude, so the 45kv coils are used to their max potential and the coil used really is 12 volts with no ballast resistor. Hotter spark in the same amount of time means leaner mixtures and more complete burn.

There is nothing arguable about this, it's just a matter of doing research and finding all of this out for yourself. I had to prove all of this when I helped create the HEI system for our vintage distributors. There just isn't any way to move forward without understanding everything there is to know about the system.

I wonder why GM changed to a "12v" coil in 1955 12v cars, but stayed with a "6v" coil in early 1955 6v trucks? "Hotter/higher" starting voltage - easier starting?

I always thought the ballast resistor decreased the voltage to around 9v?

The 1955-2nd Shop Manual does say the operating (not starting) voltage at the coil should be no higher than 7v (12v electrical system).

It's been a long time since I had mechanics class, but the best I remember from the dark ages was the the ballast resistor dropped the voltage to around 9 volts, maybe even 10 volts in some applications, not 6.

A vehicle that has been converted to 12 volt will need a 12 volt coil and the resistor. Running a 6 volt coil may work for a short time, but from what my memory tells me (and it might be wrong) it won't last long.

If things have changed I'll be glad to learn, but I know folks that have tried using a 6 volt coil on a 12 volt system even with the resistor and it didn't last long.

The only thing I can think of, is that when they went to 12 volts, it would have added confusion for the normal driver if they didn't call the parts 12 volts. Nobody wants yesterdays technology. Little did they know. You can take a 1973 C10 and put that 1950 6 volt coil on it and it will run exactly the same thanks to the ballast resistor that transfers power to heat. This is the reason I went to the trouble of researching and writing this:

http://www.devestechnet.com/Home/Native12VUpgrade

As usual I didn't do this on my own. Lots of contributors in the know.

To answer your question, the ohm value of the coil (any coil) is why the 12v system see's 5.94 volts at the points. The 6 volt system is less than that at the points. Has to do with twice the pressure (voltage) and how it behaves differently in the circuit. Ballast Resistor to 8.35 volts, coil ohm value to 5.94. With 6v system, 7.8 in, 4.87 out.

You can just plug in the numbers. Not to say that the quality of an old 6 volt coil is the same as a new 12v coil, but mathematically they are the same. Oil soaked paper between the wires vs the more modern epoxy, etc. But there are no pressure differences. The "12v coil" will last the same amount of time more or less.

All edumacation aside, best to just order parts for a 56-62 engine so there is no confusion and you get the freshest parts.

So why did GM stamp those 6 volt coil housings with big embossed lettering that read "12 volt"? I guess those engineers weren't able to read back then. A GM "12 volt" coil operates most efficiently at 9.5 volts, at least according to the training material I studied at the GM technicians' training center on Summer Avenue in Memphis, beginning in 1962.

I really don't know what I'm talking about, but I did raise a family and buy and pay off two houses with the earnings from repairing anything that rolls, floats, or flies for over 50 years.
Jerry

This is pretty simplistic, and also indicates a voltage of around 8-9 volts to the coil.

http://www.erareplicas.com/427man/wiring/ignition.htm

The voltage IS a little less than 9 volts after the ballast resistor. It is also 6 volts at the points! Just like 6 volt systems, nothing changed. But to delve into it deeper, you can take your stamped 12v coil and put it on your 6v system and it will run the same and visa versa. This has to do with mathematics that are irrefutable. No slams on anyone else, no malice on my part, just reporting the facts.

Spend a few weeks studying this with a bunch of different coils from different era's and measure voltage and resistance. Then see the differences in power and you will have no choice but to come to the same conclusion. I was told about this from an ignition system pro when creating the HEI and then studied it myself. It's not a big deal guys! You still want the 12v stamped coil on your 12v system because its newer and made of better materials. But that's the only difference. I still have all of my coils lined up with tags on them from the testing.

"The voltage IS a little less than 9 volts after the ballast resistor. It is also 6 volts at the points!"

In 100 words or less: if 9 volts from the 12v coil to the points becomes 6 volts at the points, what does the 6v coil to points become in volts?

Presumably, there would a similar reduction in voltage? If not, why not?

A similar ratio, only we are dealing with half the voltage. So if there is a 2.6 volt drop for example thru the coil with 12 volts, there will be a 1.3 volt drop with 6 volts. In theory. A person needs to prove that to themselves by measuring the voltage in three places.. 1) before the ballast resistor, 2) After the ballast resistor and 3) at the negative side of the coil which is the same as measuring at the points.

You know me by now Tim. 100 words or less isn't my specialty. The coil is a transformer and has something called a turn ratio. The number of turns in the primary determines its ohm value. Both coils (if you insist on thinking there are two) measure the same ohm value.

A good exercise just so you understand yourself how it works is to make these measurements and also measure the ohms of the ballast resistor with it out of the circuit and the coil with it out of the circuit. Then plug in the numbers.

I was surprised to learn the 6 volt coil ran the HEI system perfectly as well. Not as hot a spark as the high performance one, but kept up just fine.

The questions about 6 Volt coils and 12 Volt coils are fertile ground for confusion. So may I add to it? The difference in the ignition system between 6 and 12 Volts comes down to just one thing. Points. Some bright Engineer, very smart person, came up with a switch(that is what points are). The switch had to open and close many thousands of times per minute and...last for thousands and thousands of cycles. A lot of thinking went into this little often under appreciated part. So what do we need to know about this part? It has a limit. The limit is..current. yep them pesky Amps. It takes so much current to make the coil work(Volts be damned). Turns out the current is about 4 Amps. The switch(points) is made to handle those 4 Amps. So when the big change came to 12 Volts...The one part the "Company" did not spend money on...was the points. No I won't talk about HEI(different beast). Just how to use the 12 Volts and keep the points that worked so well? Limit the current across the contacts. So it came down to two simple fixes. 1, put a Resistor in series with the points. And 2, put a Resistor in series with the points...sound familiar? The Resistor is outside the coil if it is a "Ballast" Resistor. Common place is on the firewall and out in the air to cool(4 Amps through a little Resistance is gonna make some heat). The Resistor is inside the Coil...and presto changeo it is now a "12 Volt coil". That is how it was done. Inside equals a 12 Volt coil. Not inside...well that could still be a "12" volt coil if the Ballast Resistor was added. Or a 6 Volt coil if no Resistor is needed. Sneaky company trick? No just simple current management. Still use 4 amps to make the coil work. Still run 4 Amps through the points. Yep for those paying attention so far, the 12 Volt coil will get hot. Still have the "Resistor" to cool and the coil as well. So the question of the day? How to tell a 12 Volt(internal Resisted) coil? Measure the Resistance of the primary circuit, those funny + and - on the coil. Here is a simple to use calculator for just this kind of question: http://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.htm
So with 12 Volts and 4 Amps we get..3 Ohms at the coil(internal Resisted). And for the coil without an internal Resistor? The current stays the same, and the Volts goes to 6 Volts and the Resistance at the primary(remeber the + and - on the coil) we get 1.5 Ohms. Want to use it in a 12 Volt system? No problem, just add a 1.5 Ohm Ballast resistor. Want to use the 1.5 Ohm coil on a 6 Volt truck? No Resistor needed. Want to use that 3 Ohm coil on a 6 Volt truck? Nope, ain't gonna work(too little current to make the coil happy).

Well said Steve. I like to talk about voltage because current confuses people. Like, the current is the same throughout the circuit, yet the voltage is different. So to avoid confusion, I just stick with volts in my explanations. I didn't think to mention that there IS a true 12 volt only coil. It is the Resistor Coil which has the ballast built in. I do not like them myself. I also don't like paint melting ballast resistors!

If more than a tiny fraction of a volt can be measured at the points, clean or replace them.

THE POINTS ARE A GROUND. A GROUND MEANS ZERO VOLTS!

When the points are open, you will read full battery voltage at the side of the distributor, regardless of what the coil winding resistance and/or any extra resistors which happen to be in the circuit.
Jerry

Stop the "name calling".

Hope this is not name calling but.........back to Finkelstine.
Joe: After it stalls, try pouring a little gas into carb to see if it starts. You can't state it's not fuel related if you have not done this test. If it does not start, search Stovebolt posts and tip section and the internet to learn how to test all your electrical/ignition components. It is not that hard or greasy. When you figure out what component(s) are bad, replace with 12V stuff if you have converted. Don't worry about the "discussion" inter-twinned here. I have no problem with the sub discussion because I have screwed up a few good posts myself. But anyway, just trouble shoot your truck as if you don't know what's wrong, because you don't until you test. Don't assume that it's not fuel until you are sure. Buy a 12V coil, points are not Voltage specific, the same points are used from 30's to 60's.(6V/12V) I looked at the compatibility of 1956 235 points on O'reilly's website for that info.
Commentary: Good mechanics don't assume anything. It seems intuitive to say it starts after it "cools" but it could be starting after a fuel problem subsides. Like gas tank pulling a vacuum, float can't keep up, pump "vapor locks" or can't keep up, dirt particle re-settles. It's hard to keep an open mind when the neighbor's husband's uncle tells you something. Mechanics test first, their experience tells them where to test first. I'm not a mechanic, Jerry is/was an instructor to mechanics.

Hi Bartamos
Thank you for returning the post to some of my original questions. I did enjoy the intervening discussion a bit, but it did begin to wander. When I stalled, I did a quick test with manually moving the carb linkage to full throttle and trying to see if gas would squirt. I could not see down the throat, so I then removed the oil bath cleaner, got a step ladder (so I could actullay see down the throttle barrel) and did the test again, while I could not see the squirt ( not sure if I still had a good view) - I decided to try a squirt or two of starting fluid just to see if it would even bark on start. No luck and at this time I had to attend to a couple of things when the wife decide to pull up with a car full of groceries. By the time things settled down a bit, of course it fired right up. I have driven it now about five times and it fires right up now, so I think I am going to have to induce the problem again on purpose so I can trace it better. I am thinking now of replacing the coil, condenser, plugs, wires, distributor cap and points just so I can be certain of their status, although for the life of me, I could not find anything resembling a ballast resistor. I remember them well from my younger days, and I have seen replacement part images, so I do know what I am looking for. The truck was definatley re-wired not long ago and the wiring to the coil is confusing to me as it appears out of a harness that disappears into the firewall, leading me to beleive that if I have a ballast resistor, it must be on the passenger side of the firewall - did nto look their yet.

I now have about 5-10 hours driving here and must say I am getting more comfortable as I remember how to finesse a clutch again ( still rusty, especially on the numerous hills in my city)

Problems aside, this truck is quite enjoyable to drive and brings a smile to me every time I see her in the garage or driveway - I will get this fixed on day and also get a new flywheel as well ( grinding starter )

thanks for the help - hope this thread is useful for others

I believe you should have a wire from ign sw to ballast, out other side of ballast to coil pos and a wire from foot start switch side post to coil pos. Coil neg to dizzy. Follow coil pos wires to find ballast resistor. You do need to expose wires in harness or follow the colors and draw a diagram of how all ignition is wired, then compare to what it should be. Let us know if you need further. It is hard to fix a problem that does not appear often. From what I read the gas test was not conclusive, was interrupted and lighting and access was not good. Must confirm in order to move on. I realize the problem is not serious yet and is manageable.

If there is no external ballast resistor, or a coil with one built in, then that could be your problem.
Coils will overheat and break down without some type of voltage drop.

Not wanting to get involved with the above. Others are beating it to death.
You said you were going to exchange a bunch of parts, which is ok I guess. Many of us here would rather nail it down to one component, but that's just us.
I would suggest you install a ballast resistor if you can't find it. Also, I have had a condensor fail for heat reasons. After it cooled off it 'healed' itself as they are constructed of a wax paper like material. But you stated it was a wholesale change so it's a mute point.

HI Pre 68 and Beltfed,
Thanks for the responses. In general, I was actually going to focus on just changing the coil, condenser and ballast resistor, as I have no idea of their state and would like to eliminate them as possibilities. I may also proceed to change out the distributor cap, points, wires and plugs, but that is more driven from I am not sure of their overall condition and am at the state of waiting for another failure here. weather has been cool (50's-60's) so far in Michigan and the Truck is running fine so far. She starts immediately and runs fine since the original problem, which has not repeated

I am going to start tracing the ignition circuit to see what is going on here, as I cannot yet see a ballast resistor anywhere, unless it is in my cab - I have a harness connection coming through firewall and wire connecting directly to my coil, which also has a condenser attached to coil body. I will post images within next week or so when I get a chance to investigate further. I have not done anything yet, I am seeking opinions and things to try before I make any changes. I suspect that as the summer temps increase, this problem will occur again if I do nothing

Thanks again to all for the helpful suggestions

Joe

Look at your coil to see if it is labeled "internal resistor". If it is that the coil has the resistor built in.

I'm with the others, I like to find the problem before replacing everything and then wondering if I really fixed it???

Mike B

In perusing the thread I didn't notice where you confirmed there are points and condenser in the distributor. If you didn't do the 12v conversion, there is a possibility you have a Pertronix ignition system which could mean no ballast resistor. Pop the cap and take a look unless I missed something.

The condenser attached to your coil is likely for radio noise/RF suppression. I would take that off until all is well. It is remotely possible that it could be bad or wired wrong and affect ignition.