Do I need Ballast Resistor - JeepForum.com

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post #1 of 35 Old 07-09-2010, 07:07 PM Thread Starter
mjeckell
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Do I need Ballast Resistor

I have a 1979 cj7 v8 304. I have upgraded to a larger MSD cap, rotor, and blaster 2 coil. Spark gap at .045. I also put 8.5mm MSD plug wires in. I am still using the ford duraspark ignition module. I bought the good one they had which I believe is the borg warner brand at O'reillys. I have also ran a dedicated ground to the black wire coming off the distributor.

A mechanic today was looking under the hood and asked why I had the ballast resistor in there and I said thats what the painless wiring diagram said I needed. He said in response that would be needed if it were stock but that I have upgraded the coil, cap and rotor. He explained to me that cranking with the resistor gives me the 12v needed but running that voltage is cut around half to about 6v. He went on to say that 12v is needed for the blaster 2 coil.

What do you guys think? Is he right or would this be bad for the ignition module if I removed the resistor.

- Matt

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post #2 of 35 Old 07-09-2010, 10:57 PM
RobsCrawlin7
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i have the painless harness with the motorcraft ign system with an msd coil and team rush upgrade...been running it like this for about 3-4 months and it has been fine without the resistor

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post #3 of 35 Old 07-10-2010, 01:48 AM Thread Starter
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any other opinions?
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post #4 of 35 Old 07-10-2010, 09:27 AM
BioTex
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Doesn't the factory coil say "for use with external resistor" stamped on it? That leads me to believe the coil could fail with out it. If you have a coil designed for "no resistor", then I would think you are OK with out one.

I'm not 100% though!

'85 CJ7, BDS 4" lift, 1" Body lift, 33x12.5, Shrockworks Sliders, 304 V8 with RV cam., T-176, D300, Dana 30, AMC 20.

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post #5 of 35 Old 07-10-2010, 09:46 AM
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I think the resistor is there to keep from burning up the duraspark ignition module. At least on later years.
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post #6 of 35 Old 07-10-2010, 10:08 AM
BioTex
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Quote:
Originally Posted by VACJ7 View Post
I think the resistor is there to keep from burning up the duraspark ignition module. At least on later years.
Must be, because why else have it!

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post #7 of 35 Old 07-10-2010, 10:48 AM Thread Starter
mjeckell
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How could they build a ICM that could not handle the 12v supply. I dont understand?

Matt
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post #8 of 35 Old 07-10-2010, 11:43 AM Thread Starter
mjeckell
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What I am confused about is the resistor is right at the coil. Doesnt it just reduce the coil voltage in the run position and give 12v at cranking? If so, wouldnt the ICM always receive 12v. Little confused.
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post #9 of 35 Old 07-10-2010, 11:49 AM
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If you have an upgraded coil you shouldn't need it. I took mine out when I did the TeamRush on my truck. I'm pretty sure that the blaster coils have an internal resistor. Your best bet would be talk to JeepHammer.

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post #10 of 35 Old 07-10-2010, 11:50 AM
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Duraspark needs a resistor...it can't stand a full 12v.

HEI, as some folks convert to, you have to take the resistor out...it wants the full 12v.

Your Duraspark module will be fried with 12v.

I was under the impression that the stock resistor was a resistor WIRE, though...not that old-timey firewall-mounted resistor like shown in that diagram.
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post #11 of 35 Old 07-10-2010, 11:54 AM
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Quote:
Originally Posted by Pacfanweb View Post
Duraspark needs a resistor...it can't stand a full 12v.

HEI, as some folks convert to, you have to take the resistor out...it wants the full 12v.

Your Duraspark module will be fried with 12v.

I was under the impression that the stock resistor was a resistor WIRE, though...not that old-timey firewall-mounted resistor like shown in that diagram.
But if his new coil has an internal resistor he is just throwing another resistor in there. I wouldn't think the Ign module cares how many volts you are throwing at your coil.

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post #12 of 35 Old 07-10-2010, 12:14 PM Thread Starter
mjeckell
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That is whats confusing isnt the module always getting 12v and isnt the resistor only affecting the coil?
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post #13 of 35 Old 07-10-2010, 12:21 PM
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Quote:
Originally Posted by mjeckell View Post
That is whats confusing isnt the module always getting 12v and isnt the resistor only affecting the coil?
From what I understand and from the diagram above that is how it should work. Your 12v going into the ICM is spliced in before the resistor so therefor it should have no effect on the ICM. Probably the easiest thing to do is to give MSD a call and see what they say about running a resistor. I tried looking, but everything I can find doesn't say whether the blaster coils have internal resistors or not.

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post #14 of 35 Old 07-10-2010, 12:26 PM
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According to the MSD website you only need the resistor if you are running points. I would still give them a call though just to be on the safe side.

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post #15 of 35 Old 07-10-2010, 12:30 PM
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Quote:
Originally Posted by Pacfanweb View Post
Duraspark needs a resistor...it can't stand a full 12v.

HEI, as some folks convert to, you have to take the resistor out...it wants the full 12v.

Your Duraspark module will be fried with 12v.
.....
Wrong,
The factory duraspark HAS a resisitor in the wiring. You will be better off withOUT an added resistor.

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