Ballast Resistor for 1970 Roadrunner

[wtate]

Hi All,

Just at the tail end of my restoration of my car and was wondering if someone could help me out here. I'm switching to the orange box electronic ignition and have the complete wiring harness (engine, headlights, dash & rear) from M & H. Although the car came with a 2 prong ballast resistor, they are telling me it needs the 4 prong with the electric ignition. If I can actually change it to run the original 2 prong without too much trouble that would be great. If that is not viable, then my question is how/where to mount it that looks as factory as possible (open to suggestions) and is there a bracket for it, can't seem to find it just has hole in the middle. See attached photo.

Thanks,

Wayne

 

[RJRENTON]

Wayne,
It all depends on how many terminals are on your orange box. Most of the new designs use a 4 terminal box which will use a 2 terminal resistor of 0.1 ohm resistor and a Mopar coil. The original resistor used with a points distributor and Mopar coil was 0.5 ohms.
I'm sure others will have their own opinions and preferences and why you should use MSD ignition or even a bastardized GM HEI distributor. Its your choice. My choice is OEM Mopar or for an occasional use vehicle, points system will perform OK. I use a Prestolite dual point distributor in my origional RS23V0A****** GTX and it works just fine. Just my opinion of course. BTW....When considering a resistor, consider one with the open back, either repro or NOS. The solid back resistor, such as those made by Dale, have a tendency to overheat and fail . Just a thought. .
Bob Renton

 

[wtate]

Thanks for the info, much appreciated. I'm wanting to stick with the electronic ignition I have, see photos. Where do I get the open back ballast resistor 4 prong? All I've seen in Year One & Classic Industries with solid back ones your referring to and it's what I currently have as well (see photo)?

 

[RJRENTON]

Check out Herb's parts or Tony's parts or Kramer Automotive Specialies, or Year One or Rich Rhenberg's website, maybe the intnet. They all have web sites....Google them... The important aspect is get the correct resistance to match the coil. The transistor on the orange box is subject to fail if overloaded by incorrect coil or wrong resistor. Just my opinion of course.
Bob Renton

 

[wtate]

Check out Herb's parts or Tony's parts or Kramer Automotive Specialies, or Year One or Rich Rhenberg's website, maybe the intnet. They all have web sites....Google them... The important aspect is get the correct resistance to match the coil. The transistor on the orange box is subject to fail if overloaded by incorrect coil or wrong resistor. Just my opinion of course.
Bob Renton

Great info. Thanks, I'll make sure and get the correct Ballast Resistor.

 

[R/T Boy 67]

That orange box in the picture only requires a two prong resistor, as stated by RJRENTON.

 

[wtate]

OK, that's great to hear!!

 

[wtate]

That orange box in the picture only requires a two prong resistor, as stated by RJRENTON.

One other question. I finally found a .1 Ohm two prong ballast resistor. It's not an open back though. They do have a .08 ohm ballast resistor (2 prong) with an open back. Will this work?

 

[RJRENTON]

Wtate,
An 0.08 ohm resistor will allow the coil to draw too much current and over time, will cause it to over heat and eventually fail. The extra current must be handed by the Electonic conttol box, which will cause the switching transistor one the front of the box to over heat and eventually fail as well.
For a correct ballast resistor, consider looking at YearOne or one of the suppliers previously noted. Do not let cost be the determining factor....you are trying to build a good looking reliable car.....don't try and cut costs now...buy what's needed. Those vendors can supply what you need....approximately $ 40 (+/-) plus shipping. Just my opinion of course.
Bob Renton

 

[wtate]

Wtate,
An 0.08 ohm resistor will allow the coil to draw too much current and over time, will cause it to over heat and eventually fail. The extra current must be handed by the Electonic conttol box, which will cause the switching transistor one the front of the box to over heat and eventually fail as well.
For a correct ballast resistor, consider looking at YearOne or one of the suppliers previously noted. Do not let cost be the determining factor....you are trying to build a good looking reliable car.....don't try and cut costs now...buy what's needed. Those vendors can supply what you need....approximately $ 40 (+/-) plus shipping. Just my opinion of course.
Bob Renton

Thanks, I will keep looking, I'm not worried about the cost. I'm just not having any luck thus far finding anything through those sources but the .1 ohm resistor with the filled back. Still some to follow up with.

 

[383man]

It actually depends on the overall primary ign system ohms as the which ballast to run. And different ign coils make a difference. I have not run a ballast for the last 4 years. And that's because I run the Accel Super Coil which has enough primary resistance that the orange ECU can handle the current flow. Its not to many amps flowing to overheat the coil or hurt the ECU. So depending on coil you use can make a difference. I ran a .75 ballast for years using a stock coil and the orange ECU. I don't know what coil you use as its primary resistance will effect the primary ign current flow but if you have the 1 ohm ballast and the .08 ohm ballast either one will work fine. If you want to feel safer then use the 1 ohm or you can even get a 1.25 ohm ballast. But your spark output will be a bit less. One thing I do is run the car for a good 1/2 hr or more and then shut the eng of and feel how hot the coil is. They will get warm but if you have to much current flow the coil can get very hot. I ran my car for over 1/2 hr with no ballast and the Accel super coil using the orange ECU and the coil was not even hot. And as I said I have been running this setup with no ballast for over 4 years. But for you I would use at least the .08 or 1 ohm ballast and be fine. Also its always nice to carry a spare ECU , Ballast and coil in your trunk which I carry but have never used. Heck I even carry a spare pick-up coil in my trunk but again have never used it. Good luck with it. Ron

 

[Ranger16]

I bought a spare .05 ohm, 2 prong, open back resistor from O’Reilly Auto Parts.

 

[383man]

I bought a spare .05 ohm, 2 prong, open back resistor from O’Reilly Auto Parts.

That's fine as the stock specs for a 1976 dual ballast is .6 ohms on the coil side and 5 ohms on the auxiliary side. Ron

Again you said .05 and I think you mean .5 which is half an ohm as .05 is not even one tenth of an ohm. The specs on most of the dual ballast I see is .6 on the coil side and 5.0 on the auxiliary side. So if you mean .5 that should be ok.

 

[RJRENTON]

It actually depends on the overall primary ign system ohms as the which ballast to run. And different ign coils make a difference. I have not run a ballast for the last 4 years. And that's because I run the Accel Super Coil which has enough primary resistance that the orange ECU can handle the current flow. Its not to many amps flowing to overheat the coil or hurt the ECU. So depending on coil you use can make a difference. I ran a .75 ballast for years using a stock coil and the orange ECU. I don't know what coil you use as its primary resistance will effect the primary ign current flow but if you have the 1 ohm ballast and the .08 ohm ballast either one will work fine. If you want to feel safer then use the 1 ohm or you can even get a 1.25 ohm ballast. But your spark output will be a bit less. One thing I do is run the car for a good 1/2 hr or more and then shut the eng of and feel how hot the coil is. They will get warm but if you have to much current flow the coil can get very hot. I ran my car for over 1/2 hr with no ballast and the Accel super coil using the orange ECU and the coil was not even hot. And as I said I have been running this setup with no ballast for over 4 years. But for you I would use at least the .08 or 1 ohm ballast and be fine. Also its always nice to carry a spare ECU , Ballast and coil in your trunk which I carry but have never used. Heck I even carry a spare pick-up coil in my trunk but again have never used it. Good luck with it. Ron


View attachment 828914

I guess it all depends on how origional you want every thing to appear. The Accel super coil may function well, but it looks out of place mounted on the fender well. The same could be said for the fuel pressure regulator...
As far as coil current draw....the coil's primary resistance is a factor but not the only factor involved. Impedance is more of a factor, as it can limit current flow; so is inductive reactance during the charge/discharge cycle. Inductive reactance limits the RATE of current flow, allowing the switching transistor's collector junction to pass the instantaneous current flow to a manageable value within its design parameters. Remember, the transistor on Mopar 's orange box is On until the trigger coil does generates the off signal and in turn, the coil produces the spark pulse.
Perhaps you should consider using the GM's HEI module, which does not use a ballast resistor but even uses a coil with even better operating results. The slant 6 website totally explains the benefits of such a conversion. It can be used on a Mopar distributor very nicely. It shows via o'ccope waveforms why its a better system.....check it out for yourself.
Just my opinion of course.
Bob Renton

 

[383man]

I guess it all depends on how origional you want every thing to appear. The Accel super coil may function well, but it looks out of place mounted on the fender well. The same could be said for the fuel pressure regulator...
As far as coil current draw....the coil's primary resistance is a factor but not the only factor involved. Impedance is more of a factor, as it can limit current flow; so is inductive reactance during the charge/discharge cycle. Inductive reactance limits the RATE of current flow, allowing the switching transistor's collector junction to pass the instantaneous current flow to a manageable value within its design parameters. Remember, the transistor on Mopar 's orange box is On until the trigger coil does generates the off signal and in turn, the coil produces the spark pulse.
Perhaps you should consider using the GM's HEI module, which does not use a ballast resistor but even uses a coil with even better operating results. The slant 6 website totally explains the benefits of such a conversion. It can be used on a Mopar distributor very nicely. It shows via o'ccope waveforms why its a better system.....check it out for yourself.
Just my opinion of course.
Bob Renton

Well my car is not a stock restored type car as its a street/strip muscle car and I prefer my coils mounted on the fenderwell or firewall for less vibration. And the pressure regulator does not look out of place at all for a street/strip car and its needed since I run the Holley black pump. I never waste my time with a mechanical fuel pump on a muscle cars using todays pump gas. So to me none of it looks out of place as I think it looks great for what I use the car for and I don't see what the heck my coil looks like or my pressure regulator looks like has to do with this. Were talking about his question of a ballast resister.

And sure I agree with you about the primary current flow but the overall primary ign circuit resistance is the first thing I would consider in selecting a ballast and then the impedance and of course the ECU is a factor since it does what the points and condenser did and all of us older guys have gotten zapped by a condenser. I was not trying to be a smart a$$ but you said a .08 ohm ballast will eventually ruin his coil and I have never seen this. The stock dual ballast uses .6 ohms on the coil primary side and of course it varies a bit with temp and when the eng is running since the ballast cools some at higher speeds with less dwell build time for a hotter spark. But at room temp is call for a .6 ohm on the primary side so I cant see a .8 ballast burning up the coil. But I just realized I think I made a mistake as I am thinking a .8 ballast when he wrote a .08. So here I am thinking a .08 ballast is close to the .75 rated ballast I have used but .08 is a big difference so that may be my mistake as I agree .08 is much less resistance then it calls for. He also has to make sure he don't use a coil for MSD ign as they can have a much different primary resistance.

My point is as long as he runs a stock coil or close to it a .8 ballast should be fine since they call for a .6 on some years on the coil side of the ballast. And I have run .75 ballast many times with stock or close to stock ohm coils and never had a problem. Honestly I see a good bit of guys running the ballast by passed like I have done on their cars with performance coils. I know about years 5 ago Mopar Muscle wrote an article about by passing the ballast on the stock Mopar ign and I believe that's why many do it and I am sure some don't get away with it since it all boils down to the primary current flow. When I decided to bypass my ballast is when I started carrying a spare coil and ECU but in over 4 years its never been needed and it has a hotter spark.

I don't want to confuse the original poster but I would like to know what coil he is using and I believe a .8 (not .08) ballast will be fine as long as he is using a stock or close to stock type coil. Ron

 

[Ranger16]

Again you said .05 and I think you mean .5 which is half an ohm as .05 is not even one tenth of an ohm. The specs on most of the dual ballast I see is .6 on the coil side and 5.0 on the auxiliary side. So if you mean .5 that should be ok.

Oops, yeah I meant .5. Sorry for the confusion.

 

[RJRENTON]

The dual ballast resistor was used with the original 5 terminal control box. Yes, the resistance of the dual ballast resistor was: 0.5 ohm and 5.0 ohm respectively. The 0.5 ohm was the current limiting elrment of the coil's primary circuit; the 5.0 ohm section was a voltage divider component for the control box's electronic circuits. Later, the control box's circuitry was revised to eliminate the need for the 5.0 ohm voltage divider and its connection was eliminated from the conttol box, enter the 4 pin control box.

FYI...With regard to the comment about the coil's primary current flow, the total current flow is a compilation of resistance, impedance and inductive reactance NOT just resistance. These factors determine the rate of change of the current flow with respect to time. Intergral Calculus will show how the inductive reactance factor effects the charging time and amount and rate of the current that flows as well as the discharge time during the spark event. Just thought you might like to know....
Bob Renton

 

[383man]

The dual ballast resistor was used with the original 5 terminal control box. Yes, the resistance of the dual ballast resistor was: 0.5 ohm and 5.0 ohm respectively. The 0.5 ohm was the current limiting elrment of the coil's primary circuit; the 5.0 ohm section was a voltage divider component for the control box's electronic circuits. Later, the control box's circuitry was revised to eliminate the need for the 5.0 ohm voltage divider and its connection was eliminated from the conttol box, enter the 4 pin control box.

FYI...With regard to the comment about the coil's primary current flow, the total current flow is a compilation of resistance, impedance and inductive reactance NOT just resistance. These factors determine the rate of change of the current flow with respect to time. Intergral Calculus will show how the inductive reactance factor effects the charging time and amount and rate of the current that flows as well as the discharge time during the spark event. Just thought you might like to know....
Bob Renton

Yes Bob I agree with you on all of that for overall primary current flow. What I was saying is I like to look at the overall resistance of the primary first since its easy to check and if the ballast or coil is not in the specs we feel is ok then I would get the system resistance in specs first and then check the rest of the primary in reference to just what you said impedance and so on as you do seem to know what your talking about. You know you can tell when talking to some when they know what they are talking about.


My first post was not meant to be a smart a$$ but now that I read it again maybe it came off wrong as I did not mean for it to and if it did I appoligize. I did not understand why you came off making remarks about my coil and press regulator since it has nothing to do with this. So I am guessing you felt my post was out of line and as I said if it was I did not mean it to be. You seem like a smart guy and I don't want to fight with anyone here as I want to help some if I can as I am sure you want to. I hope all of this is helping …...wtate….. as that's what we want for him. I am still not sure he has told us what coil he is using or if he has I must have missed it. Ron

 

[RJRENTON]

Yes Bob I agree with you on all of that for overall primary current flow. What I was saying is I like to look at the overall resistance of the primary first since its easy to check and if the ballast or coil is not in the specs we feel is ok then I would get the system resistance in specs first and then check the rest of the primary in reference to just what you said impedance and so on as you do seem to know what your talking about. You know you can tell when talking to some when they know what they are talking about.
Ron,
I did not mean anything disparaging about your car.....im sure it works quite well. I guess I'm a just purist at heart, i take great pains to try and maintain authenticity appearance of my 1970 PLYMOUTH GTX.....sorry.
I do not remember if the original person noted what coil he was using either....
Bob Renton

My first post was not meant to be a smart a$$ but now that I read it again maybe it came off wrong as I did not mean for it to and if it did I appoligize. I did not understand why you came off making remarks about my coil and press regulator since it has nothing to do with this. So I am guessing you felt my post was out of line and as I said if it was I did not mean it to be. You seem like a smart guy and I don't want to fight with anyone here as I want to help some if I can as I am sure you want to. I hope all of this is helping …...wtate….. as that's what we want for him. I am still not sure he has told us what coil he is using or if he has I must have missed it. Ron