Dear All,

I do have a Dodge Power Wagon 1973, with electronic ignition. Yesterday I blew my 3rd Ballast resistor in 1000 miles. Is this normal? What is wrong in my system? It is a 4 point resistor and when it blows ignition stops which is frustrating. Help anyone?

Best wishes,

No, this is not normal. We can get to the bottom of the issue, but we need more information. Is it the low resistance side or the high resistance side that burns out? Do you have a 4 or 5-pin ignition module? What is the coil primary resistance?

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Joshua

Wow! thanks a lot, I am at work at the moment, I will measure them as soon as possible and inform you. Thank you for your quick reply.

Dear Jashua,

I have measured the resistance during lunch brake, I think my ohm meter is not accurate enough since every result is around 2 ohm. I measured the working ballast to understand which side is high resistance but one is 2.1 Ohm the other is 1.8 ohm which are very close. Anyhow the leads that has "5" on them (which looks its the high resistance side) is ok, the other side blew.
My module has 5 pins.
finally my primary coil resistance is also around 2.0 which seems odd. Does these help?

The stock coil lists a primary resistance of 1.5 ohms; the stock dual ballast is 1ohm and 5 ohm. With the ign ON, engine not running, you can check that the resistance ratios are OK by measuring the voltage at the common, hot end of the ballast, at the coil (+), and at the low end of each ballast. The 1ohm side ought to go to the + coil and and so be 6 - 8V. The 5ohm side will be 12V on an aftermarket ignition module and somewhat lower on the factory original module - for many years all replacement modules haven't used that side for anything.

If you get very little voltage (<3V) at the coil +, you're using the wrong side of the ballast. The old (pre-electronic) ballasts had a ~red hot wire inside that was prone to corrosion, the wire in the electronic ones is sealed inside. I'd very carefully check that the other ballasts really died and that the connections didn't get broken through flexing or that you had a bad connection right there.

If you've got 6 - 8 V at the coil (+), you've got things connected right - if the old ballasts are really open, all I can imagine is that they got broken by flexing the connections or by getting cooked by a big short on the way to the coil or inside the coil itself; either to (-) or ground. Coils are wear items and after 1,000,000,000 sparks or so (>>100K miles) their insulation can break down inside, sometimes the short can be intermettant, so go ahead and replace the coil and inspect the (usually blue) wire running from the ballast to the coil (+).

Did you disconnect the coil primary wires before measuring the resistance? You need to isolate one side of any component you're measuring for resistance otherwise you're measuring the resistance of the system, not the component itself.

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Joshua

I would make sure the engine has good grounds, Engine to body, engine to frame, battery to body. Then make sure the charging system is not over/under charging ( 13.5v to 14.5v).

Many times bad grounds, high resistance in a part can cause this. If you dont find anything in the grounds or charging I would replace the coil if it is old. What ever is causing it would work the coil hard so its probably a good thing to just to go ahead replace it if there is any question, or age.


Something like bad plug wires or Dizzy cap can cause the coil to have to work harder which can give the ballast a hard time. You can check the temp of the coil and when you correct what is wrong the temp should lower some. I have never seen it happen but even the ignition module could effect this. Bulkhead wiring ( wiring harness connector at the firewall) can get to where it has high resistances and give problems ( look for over heated wires, and bad connections at the pins when you take it apart. EVen the pickup in the Dizzy could effect this, and maybe even the pickup gap could effect the coil.


Have you made any changes lately, like new plug wires, different plugs, had the engine apart in any way (Left a ground loose maybe)?


Jess

Yes, in general you need to isolate any component in order measure just its resistance. For the coil, you can measure the (+) to (-) ~ 1.5 ohms,
(+) or (-) to case ought to be infinite.

In general, most common multimeters don't work very well below a few ohms. A digital multimeter (DMM) has a extremely high input resistance and so can measure voltages w/o much impact on the circuit.

A test light has a much lower resistance and sometimes is a better choice for testing since it actually will draw some power - if there's a very high resistance in a circuit, a DMM may show very near full voltage while a test light will remain dark.

Dear Jess,

I have loose plug wires most of the times. They come loose so easily. If this can be the reason I guess I first should change or fix my plug wires.

Then I will re check the ground connections.

thanks

Dear Joshua,

I disconnected them and also I am now sure the low resistance (1.2 ohm) side blew. The one that has "5" on it meant to be the 5 ohm side.

Jess[/quote]

Dear Jess,

I have loose plug wires most of the times. They come loose so easily. If this can be the reason I guess I first should change or fix my plug wires.

Then I will re check the ground connections.

thanks[/quote]




Yes you should fix any problems like that. A loose plug wire will cause the coil to have to work extra hard. You can check your plug wires with your meter and if they test good just fix the loose ends. Any rust or black marking up in the end of them and you might as well get a set.

Electrical stuff can be a pain sometimes. When the budget is tight and things have just been getting by is the worst time. I go get coils out of mid 80,s and 90 model import cars at the salvage ( Datsun,s have real good coils). I use them instead of buying Accell or MSD coils .


Chances are anything you spend you will get back in gas mileage if you get a little hotter spark going. A good set of plug wires is always worth there money. THe type that has the little wire run around the center part really help the ignition, but they are not cheap. STill about every old Slant car I get the mileage is down on it, and after a few upgrades and tuning I can always get around 20 mpg out of them, if not more. AT todays fuel prices that addes up quick.

Good hot spark, carb ajust, and timing tweaking is about all it takes. THe good hot spark is the one thats hard to get without spending, but doable. Most of the time IMport cars have good quality plug wires on them also, if you can find ones that will fit. INfact after replacing a few things on yours you might find some factory ballast resistor in the slavage (almost always better than you can buy at the store now days). INfact the Jeeps have one on the fuel pump circuit but it is only one circuit ( two wire). It looks just like the ones on the old sixties Mopars but the resistance would have to be checked.

Like I said before when you get it fixed the heat will drop in the coil, and the ballast. So you will know when you fix it. THe heat shows there is to much draw on the system. Although even when right they do run warm.

Jess




Jess

jess...that was hella helpful! been slogging through HEI posts, your explanation MADE SENSE!

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1962 dodge lancer GT

A bit of info and and opinion.

My '73 D100 is also hard on ballast resistors and I think it's due to its location. If it happens to be raining when you open the hood, it dumps water on the ballast, and if it's hot at the time it could be subject to damage.