12v Conversion and Ignition coil

[chance9888]

So guys, I've decided to bring up my PW to 12v negative ground. It was originally 6v +. How do I go about wiring the ignition coil? Does it need to have a ballast resistor? If so, where? Do I need to change my ignition to one with a 'start' so-to-say turn point? I'm still using the foot starter, but honestly, I have no idea what i'm doing. If possible, please direct me on where to hook up my whole ignition system. I've been looking for a wiring diagram, but I can't find one anywhere

[Charles Talbert]

So guys, I've decided to bring up my PW to 12v negative ground. It was originally 6v +. How do I go about wiring the ignition coil? Does it need to have a ballast resistor? If so, where? Do I need to change my ignition to one with a 'start' so-to-say turn point? I'm still using the foot starter, but honestly, I have no idea what i'm doing. If possible, please direct me on where to hook up my whole ignition system. I've been looking for a wiring diagram, but I can't find one anywhere

I can help you if you will give me a call. # info is on the website below.

[Gordon Maney]

So guys, I've decided to bring up my PW to 12v negative ground. It was originally 6v +. How do I go about wiring the ignition coil? Does it need to have a ballast resistor? If so, where? Do I need to change my ignition to one with a 'start' so-to-say turn point? I'm still using the foot starter, but honestly, I have no idea what I’m doing. If possible, please direct me on where to hook up my whole ignition system. I've been looking for a wiring diagram, but I can't find one anywhere

A 12 volt system uses a ballast resistor. The purpose of it is to increase point life. It reduces primary current flow at low engine speeds. I can explain how later, if you are interested.

The ballast resistor can take two forms. It can be a separate resistor mounted in view [….like on the fender well], or it can be an integral part of an ignition coil. There have been applications where the ballast resistor is inside the coil. The most common scenario is the separate component.

Let's consider the common method — the external resistor. There is a need to implement a ballast resistor bypass. This is a function that occurs during cranking. You want your ignition system's available voltage to be as high as possible, since the current draw of the starter motor will cause a drop in battery terminal voltage. Once the engine starts, the starter motor is no longer drawing current from the battery, allowing battery terminal voltage to rise to normal levels.

In some automotive circuits this bypass has been possible due to the design of the ignition switch. When the key is turned to the start position, a terminal on the switch is provided full battery terminal voltage. That terminal is connected by means of a wire to the battery-side, primary terminal of the coil. In this situation, the starter uses a solenoid to shift the starter drive into engagement with the flywheel.

The alternative method involves a terminal on a solenoid in the starter circuit. That solenoid may either be one on the starter, or it may be mounted under the hood. When the core shifts in the solenoid, a terminal is connected to full battery terminal voltage. That terminal is connected by means of a wire to the battery-side, primary terminal on the coil. In this situation, the solenoid is serving only as a switching device, since your starter has its drive shifted by manually moving the fork.

Primary terminals on coils are marked + and -, or dist and bat. One of these terminals will have the battery voltage connection and the other will be connected to the distributor. No matter how you connect those primary terminals the engine will start and run. One way will be correct and the other way you will have incorrect polarity. Meaning, polarity of the coil, which determines polarity of the spark plug.

If you have disassembled a vehicle that has all original parts, and the coil is marked dist and bat, then there are your answers. If it has + and – then you find yourself lost in uncertainty.

I am leaving here for a while to go get something very vital. I am assembling an issue of the magazine and I have run out of Diet Pepsi. You see my dilemma.

More later on coil polarity…..


Note: If my coil polarity was incorrect, I could still drive it to town to get Pepsi. Nothing would be ruined.

[Gordon Maney]

Regarding ignition polarity, the way I always tested it in my automotive program was with the oscilloscope. If the polarity was correct, the plug voltage spike would point up. If polarity was wrong, the spikes would point down. Reversing the primary leads on the coil would correct it.

The 12 volt coil you choose to use will be new. It will be marked + and -, and will be produced during a negative ground era. Most of the references you find will tell you to connect the primary terminal marked with the negative symbol [-] to the distributor. The logic there is that the distributor will ground the primary circuit when the points close; it is a negative ground circuit/system.

Let's say you wonder. How could you test it when you have no scope? Two methods come to mind. A classic, old time method involves a wooden pencil. A carpenter pencil, if have one, since it has such a big lead.

The procedure is this: Disconnect a plug wire from its plug, then hold the pencil lead between the end of the plug wire and the spark plug electrode. If the spark flares between the pencil lead and the spark plug, the polarity. If the spark flares between the pencil and the plug wire, the polarity is incorrect.

Another method involves the use of an NE-2 neon bulb. I just did a web search and an electronics supply house had them available for $0.35. You could afford several, one for the garage and one for your vacation home.

The procedure for the neon bulb involves connecting one terminal on the neon bulb to the spark plug's plug wire terminal [plug wire connected] and the other terminal of the bulb to ground. With the engine running, the electrode in the neon bulb connected to the spark plug wire and plug terminal should glow. If the bulb's terminal connected to ground glows then polarity is wrong.

I will tell you that I have tried the pencil method several times. It is a stimulating experience if you are not careful. It is not my method of choice, but it has been commonly used, since it requires no test equipment. I think, as you can see, the 35 cent bulb would be a cheap tester. You would have to make up a slender test lead to insert between the plug porcelain and the wire's dust boot. If you just get the end touching the wires metal terminal, it will be fine. We're not powering up a high current draw motor, we are just exciting a tiny bulb.

I never had much luck getting students to try the pencil test. They were suspicious, and then when I said it would help if they connect a jumper cable from their belt buckle to a water pipe they lost all interest.

[Gordon Maney]

You will have some other issues pertaining to instruments. Your ammeter's capacity will be too low — you will peg it hard at times. Disconnect it and use a voltmeter. Also, your 6 volt, positive-ground fuel gauge won't work.

[Gordon Maney]

Interesting tool linky

I have not seen one of these before. It offers another alternative.

[chance9888]

Thank you, Gordon. ... ...However, that isn't so much my problem. I learned how to hook up the ignition coil, and all that jazz, I'm just curious because although my coil is a 12v coil it gets hot (really hot). Then I assumed I would need to put a resistor in line. After I put the resistor in line, I was trying to crank it. Of course, I understand that I'm supposed to have two wires running to the coil; one for cranking, and the other for idling/running conditions. However, I had read somewhere on DPW forums that the main cranking wire isn't really essential, and I would usually be fine without it. This was great until I tried to crank the engine and the whole ballast started smoking. I understand that they will get hot, but I wasn't too sure about the smoking.

A few other notes: My ignition is an on/off flip switch, and I called the Ballast resistors's manufacturer (duralast) and left a message under customer support about the smoking. Tomorrow, they should reply with an answer if it usually smokes during it's break-in period or not.

EDIT: Also, this is actually a different truck; not my tan 1949. This is a red (either 1946 or 1950. Previous owner says 46, but the paperwork I think for it says 1950). It's going to be a farm truck, so overall, i'm not too concerned about the gages working. I'm just going to put in an external tach and cruise like that. Also, I am putting a marine-grade, steel fuel tank in the upper right corner of the bed. It has a float level gage on the cap.

[Gordon Maney]

Thank you, Gordon. ... ...However, that isn't so much my problem. I learned how to hook up the ignition coil, and all that jazz, I'm just curious because although my coil is a 12v coil it gets hot (really hot). Then I assumed I would need to put a resistor in line. After I put the resistor in line, I was trying to crank it. Of course, I understand that I'm supposed to have two wires running to the coil; one for cranking, and the other for idling/running conditions. However, I had read somewhere on DPW forums that the main cranking wire isn't really essential, and I would usually be fine without it. This was great until I tried to crank the engine and the whole ballast started smoking. I understand that they will get hot, but I wasn't too sure about the smoking.

A few other notes: My ignition is an on/off flip switch, and I called the ballast resistors' manufacturer (Duralast) and left a message under customer support about the smoking. Tomorrow, they should reply with an answer if it usually smokes during it's break-in period or not.

The ballast resistor is needed because it is a 12 volt system.

The ballast resistor bypass is important; I would not say you would be fine without it.

There is no break-in period for a ballast resistor.

[chance9888]

perfect. Beautiful answer!

[Gordon Maney]

A bit more.....

There are two terms that apply here. Available voltage and required voltage. The voltage to fire the plug, to jump the gap, is required voltage. It is the amount of voltage required to overcome the resistance offered by the plug gap in the face of existing combustion chamber pressure.

Required voltage can vary, and is determined by plug gap size, plug terminal condition, combustion chamber pressure, plug wire resistance, coil wire resistance, rotor air gap, and secondary circuit connection quality. An open plug wire can significantly [to infinitely] raise required voltage. Open meaning it does not test as having continuity with an ohm meter — an open circuit. Resistor plug wires typically have about 10,000 ohms per foot when new, and the measured value can increase over time, particularly if they are bent repeatedly.

Available voltage is the maximum amount of voltage the system can produce. Imagine if the system is connected to a scope. If you disconnect a plug wire, that cylinder's circuit suddenly has an infinite air gap. That circuit will not be able to produce a spark, but it will try by building up the highest voltage it can. To have a spark, available voltage has to be higher than required voltage.

Available voltage is determined by [not in any particular order] battery terminal voltage, dwell angle, breaker point condition, and primary circuit resistance. [....the ballast resistor is included in primary circuit resistance.]

Dwell angle is number of degrees of distributor rotation during which the points are closed. The larger the dwell angle the higher the available voltage. The larger the dwell angle, the shorter the point life.

The ballast resistor limits primary current flow at low speeds. At low speeds the points are closed for longer periods of clock time, each time they close. That causes them to heat up and wear more. As current flows longer at low speed the resistor heats up, its resistance value increases, causing it to reduce primary current flow, extending the life of the points.

As engine speed increases, the points are closed for less clock time and the resistor cools, reducing the resistance value and allowing more current flow.

During cranking, battery terminal voltage drops, which causes available voltage to drop. Hence the need for the ballast resistor bypass during cranking, to keep available voltage as high as possible.

People sometimes ask how many volts are produced at the spark plug, and you occasionally read about high performance coils that produce higher voltages. If you ask the question, how many volts are produced at the spark plug, the answer is enough. Enough to overcome the resistance offered by the air gap of the plug. It varies, depending on the factors I mention above.

A high performance coil can raise available voltage, but it will not raise required voltage, therefore it does not cause hotter sparks. That is marketing language. If you increase plug gap, that will cause a hotter spark.

If required voltage exceeds available, there will be no spark.

[chance9888]

ok, so what advice do I need as far as putting in the wire to bypass the resistor? How can I make it so that wire is only used when I am starting the truck/what can I use to control that wire? Charles Talbert says it's just a better idea to get a coil with internal resistance, which is I agree is good, but I already have my coil and a resistor, and so if it's at-all possible to hook it up now, i'll try it.

Also, I think the reason the resistor was smoking could have just been the large amount of current being pulled through it. The battery was loaded, and the coil may have just been needing too much power

[Gordon Maney]

ok, so what advice do I need as far as putting in the wire to bypass the resistor? How can I make it so that wire is only used when I am starting the truck/what can I use to control that wire? Charles Talbert says it's just a better idea to get a coil with internal resistance, which is I agree is good, but I already have my coil and a resistor, and so if it's at-all possible to hook it up now, i'll try it.

Also, I think the reason the resistor was smoking could have just been the large amount of current being pulled through it. The battery was loaded, and the coil may have just been needing too much power

What are you using for a starter? The original, foot controlled one, I assume? If so, you can't implement the bypass from a solenoid in the starter circuit. There is no solenoid in that starter circuit.

You can make the argument that you can get along without one, but I am not sure I would want to go with that for cold starts in hard cold. The remaining way is to use an ignition switch that offers a ballast resistor bypass function. NAPA should offer such a switch. In cases where it was thought the bypass could be necessary, you would turn your ignition switch to the start position as you cranked. Most of the time you could simply not choose to do that. I do not believe you can implement a ballast resistor bypass function with a coil having an internal ballast resistor.

[Gordon Maney]

Your starter

One other issue. I am assuming you are going to use your 6 volt starter. That is OK. But, you need to get new bushings and brushes in it. For sure. It needs to be in optimum condition. The state of tune should be good so you don't have extended cranking.

[chance9888]

Ok. Is it possible to wire the 6v foot starter so it uses the turn of a key or would I need a starter relay. And this would mean I need to find an ignition with a starting position. I assume I could just go pull one of those off of any car at a scrap yard somewhere.

[Gordon Maney]

Ok. Is it possible to wire the 6v foot starter so it uses the turn of a key

No, because that starter has no solenoid. Your choice to depress the foot rod closes the starter switch.

or would I need a starter relay.

No, you could not do that because you have to manually operate the fork for the starter drive. I believe there is a later starter you could get that would be solenoid shifted. At some point the foot rod went away. Others here may comment on when; I don't know as I sit here.

Note: I edited something I posted earlier. [I had erroneously posted that your starter has an inertia drive, but it has an overrunning clutch drive that is shifted by the manually operated rod connected to a fork. Sorry. Too tired to think straight.]

And this would mean I need to find an ignition with a starting position. I assume I could just go pull one of those off of any car at a scrap yard somewhere.

No, not any car, as not all cars used the switch to implement. That is why I mention a universal switch you get from someplace like NAPA. Have them look at their product guide, and you may have to look at the terminal markings.