Educate me on ballast resistors?

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MrJLR

MrJLR

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1968 Barracuda notch-back

PO swapped out the /6 for a 318....and I believe changed it to electronic ignition.
I was told my ballast resistor is wrong for my year....

So.....what the heck is the purpose of the ballast resister (I come from Chevys...)???
Do I have the wrong one?
If so - what is the correct one?

Sorry....I have a learning curve on these cars!

Thanks!

:burnout:
 

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Whoever converted that "was" a fair amount of time ago

The earlier Mopar box had to have a dual ballast, it's actually two (different) resistors in one, and is known as a "5 pin box."

The later box looks exactly alike but the "5th" pin is a dummy, and it only needs a 2 terminal resistor. This is known as a "4 pin" box

Only way to tell the boxes apart is to check resistance of the 5th pin to see if it's connected to anything else.

Having the older 4 pin ballast on a newer box doesn't hurt anything, it's simply that the "other half" of the resistor does not do anything.

There has been some change in resistance over the years, but in essance there are only two resistors all these years. The "coil side" of the 4 terminal resistor is the same resistance as a 2 terminal resistor.

===========================

Also, "for you Chevy guys," Chevies ALSO had ballasts before the advent of HEI. It was a resistor wire run in with the harness instead of a "block" resistor. 55-57 Chevs did use a block resistor, I'm not sure when Chev went to the resistance wire anymore.

Ford, AMC, and GM all had a separate "I" terminal on the starter solenoid to BYPASS the resistor for starting.

"Ma" does this in the ignition switch, that's the brown hooked in there to the coil + side
 
Interesting stuff! Thanks.....!

I'm told to always keep a spare...LOL!
I guess it's all part of the charm of these cars!

:burnout:
 
If you "come from Chevys" then you should be familiar with ballasts. Although they didn't use a resistor per say, they all had a resistor wire that fed the positive side of the ignition coil reducing voltage from 12 volts. Never seen a pre HEI GM that didn't have one, actually, and I have owned a pile.
 
RustyRatRod said:
If you "come from Chevys" then you should be familiar with ballasts. Although they didn't use a resistor per say, they all had a resistor wire that fed the positive side of the ignition coil reducing voltage from 12 volts. Never seen a pre HEI GM that didn't have one, actually, and I have owned a pile.
Click to expand...

Well, I'm used to HEI, but was educated here that there was a ballast in the harness I was unaware of!

:burnout:
 
^^ I was just gonna say that about Chevy ballast wire.....

The single ballast resistor and the low resistance side of the dual ballast is a form of current regulator. (The term 'ballast' used used to mean just that in older electronics.) The resistance actually varies with the amount of average current through the ballast.

This allows the coil current to be set nominally higher than what the coil would survive to counteract the natural drop of average coil current at high RPM's. The ballast will then lower the average coil current at low RPM to keep the coil from burning up. It also puts extra current in the coil when cold for better cold start spark energy.

BTW the old Ford V8 flatheads did not have a ballast; the static coil current was set for adequate sustained spark output at high RPM's, and depended on the regular interruption of the coil current by the points with the engine running to control the average coil current. If you left the key in RUN but the engine not running, the coil would burn out in short order. A ballasted system was a innovation 'back in the day' to cure this problem.

The main ballast in a Mopar (single or dual ballast) should be 0.5 to 0.6 ohms cold, and a bit over 2 ohms hot. There are a lot of other ballast resistors sold that have higher resistances and they will badly weaken the coil spark. (I have to wonder how many coils were replaced and system converted because of the wrong ballast.) The BWD RU19 is a pretty close equivalent sold in box stores; it has about the same cold resistance but a hot resistance of 3-3.5 ohms. The most common Mopar single ballast is PN 2095501; if you can find one, they work noticeably better in the single ballast systems with a stock type coil., especially on cold starts.
 
I have the newer mopar electronic ignition (orange box) and the single ballast resistor, so i'm guessing yes you do. someone correct me if i'm wrong.
 
nm9stheham said:
^^ I was just gonna say that about Chevy ballast wire.....

The single ballast resistor and the low resistance side of the dual ballast is a form of current regulator. (The term 'ballast' used used to mean just that in older electronics.) The resistance actually varies with the amount of average current through the ballast.

This allows the coil current to be set nominally higher than what the coil would survive to counteract the natural drop of average coil current at high RPM's. The ballast will then lower the average coil current at low RPM to keep the coil from burning up. It also puts extra current in the coil when cold for better cold start spark energy.

BTW the old Ford V8 flatheads did not have a ballast; the static coil current was set for adequate sustained spark output at high RPM's, and depended on the regular interruption of the coil current by the points with the engine running to control the average coil current. If you left the key in RUN but the engine not running, the coil would burn out in short order. A ballasted system was a innovation 'back in the day' to cure this problem.

The main ballast in a Mopar (single or dual ballast) should be 0.5 to 0.6 ohms cold, and a bit over 2 ohms hot. There are a lot of other ballast resistors sold that have higher resistances and they will badly weaken the coil spark. (I have to wonder how many coils were replaced and system converted because of the wrong ballast.) The BWD RU19 is a pretty close equivalent sold in box stores; it has about the same cold resistance but a hot resistance of 3-3.5 ohms. The most common Mopar single ballast is PN 2095501; if you can find one, they work noticeably better in the single ballast systems with a stock type coil., especially on cold starts.
Click to expand...

I don't know if all but some ballast resistors have the ohms stamped on the back. Would this be the hot or cold rating?
 
Cold. No way to measure it when hot, other than voltage checks and "some math" LOL

According to "MyMopar"

The older 5 pin box:

Notice the "U" shaped cutout in the diagram. This is on the ceramic, and shows the orientation so you don't reverse the two resistors Notice that one end, both terminals are jumpered. This is where 12V is connected

Ignition_System_5pin.jpg


Newer 4 pin box. Notice that essentially the left side of the dual ballast has been eliminated, along with the one pin in the box

Ignition_System_4pin.jpg


Specs for ballast resistors are in all the shop manuals in the very back of "section 8," electrical

From MyMopar

http://www.mymopar.com/index.php?pid=115

The one thing to remember, tho, is that the LOWER the resistance you are checking, the GREATER chance for errors due to probe problems or poor connections, and the LESS accurate your meter is likely to be.
 
That's good information to know. The one post on here says 0.5 - 0.6 ohms is best. I checked my ballast resister from Summit and it is stamped 1.25 ohms. Is this too high?
 
Lammio said:
That's good information to know. The one post on here says 0.5 - 0.6 ohms is best. I checked my ballast resister from Summit and it is stamped 1.25 ohms. Is this too high?
Click to expand...

I just realized that link from MyMopar must be wrong. Typical coil resistor (ballast) is about . 5--.6. The 1.2 or so is for the ECU on the dual ballast.

"Optimum" resistance depends on what coil you actually have. The resistor specs are in the back of all the shop manuals
 
Lammio said:
That's good information to know. The one post on here says 0.5 - 0.6 ohms is best. I checked my ballast resister from Summit and it is stamped 1.25 ohms. Is this too high?
Click to expand...
For most stock and stock replacement coils, yes.

What coil do you have? Exact model is needed, including a PN if possible. I'll venture to guess, based on the behavior of other ballasts, that the 1.25 ohms cold ballast will rise to about 5 ohms hot, and the coil current (and thus spark energy) for most coils will be low with that. The most common original Mopar ballast is a bit over 2 ohms hot.

You'll be somewhat better off with most coils with a BWD RU19 ballast from the box parts stores than the 1.25 ohms cold one; you will be getting closer to what the system was designed for. High ballast resistance can/will effect warmup situations from a cold start; the engine will run great for 10-30 seconds and then get a bit rough for a while until the engine gets good and warm. High ballast resistance can also effect high RPM firing.

One common ballast I see on a lot of cars is 2 ohms cold and 7 ohms hot; that reeeeally effects things adversely. Below is a pix of the 'bad one', the one with the rounded mounting tab, and the better BWD RU19, with the angled edge mounting tab. As noted before, the original Mopar is best with a stock type coil; it has the correct resistances cold and hot that the Chrysler system was designed for; my /6 ran pretty much perfectly in cold Jan starts with the original Mopar ballast, the RU19 was decent but a bit rough, and the cold start went to crap with the RU4.
 

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I've always run the MSD Blaster 2 coils. Sorry don't know the pt # off hand.
 
Thanks for all the info. Unfortunately whenever I've asked the guys at the big name parts stores about ballast resistors they say "they're all the same". I figured they weren't but didn't know why. You've explained a lot. Thanks again.
 
My 67 Dart has the same 4 pin ballast resistor as your 68 barracuda. When I got the car it still had the points distributor and the tiny voltage regulator. The wiring had not been touched.
 
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