You are now the expert.  Try it and report back with your findings!

If the Red grommet has this capability of burning better, why is the Blue grommet used for hot rod conversions?

Blue grommet uses the horseshoe connector type coil connector.

What kind of terminals are on the Red grommet coil?

Ages ago I called Borg Warner, one of the primary manufacturers of the Duraspark II modules to ask if they needed a full 12V to work properly.  During that conversation the engineer told me about the red gommet model being used in higher performance vehicles (e.g., law enforcement, etc) and that it provided a hotter spark, and that it tended to run hotter and not last as long as the blue grommet module.

I don't have any experience with any of the modules other than the one with the blue grommet but thought I'd pass along the information.

I confess that I don't fully trust my blue grommet module either.  I have 2 spares in the trunk, just in case.

Last edited by John Ha (4/21/2020 4:15 PM)

I am thinking that way back when, for the wiring diagram, I went to a junk yard and all the cars had blue strain relief modules, because that is what was supplied in Texas cars. Never occurred to me that there was any other way to do it. I just wanted to figure out how to put a Duraspark in my car.  I am sure I was NOT the first one to do it, but I did a drawing and posted it. Bradster, a forum member st the time, did an enhancement of the drawing that looked pretty good, so it got posted on my website.  (I later noticed some diodes and stuff not needed to wire it in his drawing, but it still remains on the website).   I have since learned more about it from those electrically gifted ones on FYIFORD, but the original drawing with blue strain relief remains.  It gets the job done for those who want a reliable distributor and ignition system.

I am using a Duraspark II distributor on my 427 with modified bushings in it, even though I ditched the blue module system for an MSD 6a box.    On my 56 F100 with a 2001 5.0, I am using a stock replacement Duraspark II distributor and stock module with a blue strain relief. 

If you try the other one and it works out better, post the results and maybe a footnote can be added to the website drawing.

Rufus68 wrote:

I'm going to throw in my 2 cents regarding the resistor wire and if my understanding is wrong then I'd like to know the correct information as well.

The coils that Ford used to use years ago would get too hot when operated continuously using 12 volts.  And since the engines would run just fine with the coil powered by 6 volts, the engineers decided to put in a resistor wire to drop the voltage to not overheat the coils.  However, they found that the engines started much easier when the coil was powered by 12 volts so they added the "I" terminal to the starter solenoid to temporarily power the coil with the full 12 volts while cranking the engine. 

With this in mind, one should use a resistor to drop the voltage if and when they are using an old style coil that overheats from continuous 12 volt operation.  If the coil is made to operate on 12 volts, then 12 volts should be fed to it to produce the intended spark.

That's pretty much it in a nut shell. The only thing I would add is, don't buy a 12 volt coil and get rid of your resister if you are still running points. They could make 12 volt coils back then but the higher voltage was hard on the points too.

I used an Accel Blueprint Duraspark distributor, Jacob’s Electronic Mileage Master ignition and Ultra coil with the 289 setup.

I probably could have easily used the Duraspark ignition with same results, without the cost.
Also used a connector from junkyard to directly plug into stock Duraspark distributor.
Plug and play of the 90’s for me.

My wife’s 79 F150 still has stock Duraspark ignition.
Started up without problems after sitting in winter storage.

MS wrote:

Apparently, Duraspark ignitions all had 12 volt coils.
My recommendation is wire it for 12 volts and use a 12 volt coil. Hook up both the red and the white wire as intended.

The second wire that only receives power while cranking on a Duraspark is solely to provide (internally within the module) a retarded timing while cranking to make it start easier. It is NOT like the second wire on points systems that existed to provide 12 volts while cranking to get a hotter starting spark.

From what I have read in the past, with points systems, voltage drops from whatever reason caused points to burn up, so a more consistent current could be maintained if the voltage was lowered.  I am not an electrical engineer, but I know lower voltage requires higher current. That can damage contacts.  Someone else with more electrical knowledge can confirm, deny or ridicule...

The spark from the coil is produced when the circuit is opened. It's the sudden collapse of the magnetic field being cut by the copper winding. Just as you have a spark produced in the secondary winding you have a similar spark in the primary winding and across the open points. The purpose of the condenser is to conduct this voltage spoke to ground instead of across the points. It's that arc that pits the points.

For a given resistance, when you cut the voltage in half, you have reduced amperage in half. Wattage is voltage x amperage. So by reducing voltage in half, wattage or power is not one half but one forth. Cutting voltage across the points from 12 volts to 6 volts means the total power the points have to handle is substantially reduced.

My factory Ford coil on my factory Ford module calls for a ballast resistor. The Duraspark does not supply the coil with power but rather open and closes the ground side of the coil. This is typically done with electronics since they can "sink" or ground more power safely then they can supply or "source". Just like the points the electronics have to handle the coil power. Now running a coil on 12 volts instead of 6 volts, it means the Duraspark module must handle quadruple the power and quadruple the heat.

If you have a 6 volt coil on 12 volts doesn't necessarily mean output voltage is going to be doubled. At some point the coil is going to be saturated and any increase in primary voltage won't have a proportional output.

Huskinhano wrote:

Rufus68 wrote:

I'm going to throw in my 2 cents regarding the resistor wire and if my understanding is wrong then I'd like to know the correct information as well.

The coils that Ford used to use years ago would get too hot when operated continuously using 12 volts.  And since the engines would run just fine with the coil powered by 6 volts, the engineers decided to put in a resistor wire to drop the voltage to not overheat the coils.  However, they found that the engines started much easier when the coil was powered by 12 volts so they added the "I" terminal to the starter solenoid to temporarily power the coil with the full 12 volts while cranking the engine. 

With this in mind, one should use a resistor to drop the voltage if and when they are using an old style coil that overheats from continuous 12 volt operation.  If the coil is made to operate on 12 volts, then 12 volts should be fed to it to produce the intended spark.

I'm going to disagree with that. It's no problem designing a coil to work on full 12 volts and not over heat. There is a lot involved in designing a coil. In a nut shell running a resistor in line to the coil allows for a nice advantage. You can get the needed spark at 6 volts. If you ran a 12 volt coil, when you crank the engine there is a big inrush of current to the starter. As a result battery voltage drops significantly. If you had a 12 volt coil, while cranking the engine battery voltage may be in the 6-8 volt range. That would result in a huge drop in spark quality. But running on 6 volts on a 12 volt system with a resistor when the starter is engaged, the resistor wire is bypassed and the coil now gets what ever the battery voltage is. So if the battery voltage drops to 6-8 volts, it's basically the same voltage the coil normally sees along with a hot spark.

Running a 6 volt coil on a full 12 volts may not increase spark output and just make the coil run hot. For a given resistance, doubling voltage quadruples the heat it has to deal with. Resistance or more correctly impeadence of a coil also depends on the frequency of the power or in this case, RPM. At some specific point a coil will stop functioning.

Never thought of it that way but it makes sense. I was always told lower voltage to save the points. Use a lower voltage coil to save the points. Bypass the resister at start to make up the voltage drop from cranking the large starter motor. Just out of curiosity I checked my 5 year old battery voltage while cranking my engine.  Got about 10.5 volts. Not 6 or 8 volts, but battery technology is probably better today.

MS wrote:

Ohms Law says if voltage is halved, current amperage doubles. Wrong?

I'm not an electrical engineer nor do I play one on TV but I'll give this a shot.
Amps * Volts = Watts. Watts is basically the work you will get out of electricity. If you lower the voltage you will need more amperage to produce the same wattage or work. This is not usually the case. Think of a light dimmer switch. As you lower the dimmer switch you lower the voltage, lower voltage pushes less amps. Lower voltage less amps produce less watts, the light goes dim. Think of it this way, voltage is pressure and amps are electricity. You have an air compressor set at 25 lbs. It will push a certain amount of air through your hose. Crank the pressure up to 50 lbs and you will push twice as much air through the hose. The air is amps the pressure is volts.

Now that's the simple explanation. Getting back to your first question, less volts mean more amps. An AC motor speed is dependent on the frequency of the system. Our system is 60 hertz. Single phase AC motors are usually 1 speed, speeds are usually a multiple of 60. Sense an AC motor is single speed and dependent on frequency, if voltage drops it will draw more amps to maintain its speed and do the same work. This is why if the voltage lowers to much the motor will draw enough amps and burn up. 

Hope this helps.